KKGvSl  v7G9I 

College  of  ^tjpsiiciansi  anb  burgeons; 
itibrarp 


Dr.  C.  F.   M^^cPo-rv^^.l<i. 


A  MANUAL 


OF 


DENTAL  PROSTHETICS 


BY 

GEORGE  HENRY  WILSON,  D.D.S. 

FORMERLY    PROFESSOR    AND    DEMONSTRATOR    OK    PROSTHETICS    AND    METALLUROT    IN   THE 

DENTAL   DEPARTMENT    OF    WESTERN    RESERVE   UNIVERSITY, 

CLEVELAND,    OHIO 


TllluetratcD  witb  396  Bngtavings 


LI:A   it    FEHTGER 

I'll  I  LA  UELFII  I  A    AND    N  10  W    YORK 


Entered  according  to   Act  of  Congress,  in  the  year  1911,  by 

LEA    &    FEBIGER 
in  the  Office  of  the  Librarian  of  Congress.      All  rights  reserved. 


THIS  VOLUME 

IS    DEDICATED    TO    THE    MEMORY    OF    THE    LATE 

JONATHAN  TAFT,  D.D.S.,  M.D. 

AS  A  TOKEN'    OF   RESPECT  AND  ADMIRATION   FOR   THE   LIFE  AND 

WORK    OF    THE    EMINENT    TEACHER,    PROFESSIONAL 

MAN,   AND    CHRISTIAN    GENTLEMAN 

THE  AUTHOR 


Digitized  by  tine  Internet  Arciiive 

in  2010  witii  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/manualofdentalprOOwils 


PREFACE 


This  book  has  been  written  in  response  to  the  oft-repeated 
request  by  teachers  and  members  of  the  dental  profession 
for  a  concise  modern  text-book  on  Dental  Prosthetics.  It 
is  the  result  of  the  experience  gained  in  thirty-f^^'e  years 
of  practice,  fifteen  years  of  which  have  been  devoted  exclu- 
sively to  prosthetics  and  thirteen  years  to  teaching  in  dental 
colleges.  The  author  hopes  it  may  meet  the  requirements 
and  merit  the  approval  of  both  teachers  and  practitioners. 

The  desire  has  been  to  give  the  physical  and  chemical 
properties  of  the  materials  used  in  as  terse  a  form  as  con- 
sistent with  thoroughness,  and  also  to  explain  the  technique 
sufficiently  in  detail.  Repetitions  and  the  recital  of  multi- 
farious methods  for  accomplishing  the  same  end  have  been 
avoided.  However,  it  has  seemed  wnse  in  some  instances  to 
vary  from  this  intention  as  instanced  by  the  space  given 
to  the  writings  of  Prof.  Gysi.  This  plan  renders  it  necessary 
for  the  reader  to  peruse  the  chapters  in  order,  and  to  refer 
often  to  the  index,  which  has  been  arrangefl  to  faciHtate 
correlation  of  the  various  phases  of  each  subject. 

If  it  appears  that  credit  has  not  been  gi\<Mi  freely,  it  is 
l)ecau.se  the  author  makes  no  claim  to  originality,  and  is 
recording  methods  and  ideas  which  he  has  acquired  from 
sources  too  wide  to  trace.  Their  inclusion  has  not  flepended 
on  their  origin,  but  solely  on  their  j)i-ov('d  \aliie  in  j)ractice. 


VI  PREFACE 

The  author  long  since  learned  that  it  is  hazardous  for  any 
man  to  claim  originality,  as  we  are  all  dependent  one  upon 
another.  At  times  he  may  seem  arbitrary  and  critical, 
but  he  is  pardonable  if  he  has  succeeded  in  making  clear 
a  truth  or  impressing  a  fact  in  the  reader's  mind. 

The  author  wishes  to  express  his  thanks  to  all  who  have 
so  generously  permitted  the  use  of  material  or  furnished 
illustrations.  He  desires  especially  to  mention  his  indebted- 
ness to  Dr.  Charles  R.  Turner,  Prof.  A.  Gysi,  and  Dr. 
George  B.  Snow  for  the  use  of  their  writings;  to  Dr.  Chalmer 
J.  Lyons  for  illustrations  of  the  cleft  palate;  to  Dr.  Harris 
R.  C.  Wilson  for  drawings;  to  Dr.  Guy  D.  Lovett  for 
reviewing  the  manuscript;  and  to  the  publishers  for  many 
courtesies  shown. 

G.  H.  W. 
Cleveland,  Ohio,  1911. 


CONTENTS 


CHAPTER  I 
The  Mouth ^^ 

CHAPTER  II 

Impressions ^^ 

CHAPTER  HI 

Casts 


109 


CHAPTER  IV 
Occlusion  and  Contour  Models  ....     123 

CHAPTER  V 

Articulators  and  Antagonizors  ....     165 

CHAPTER  VI 

Rubber  and  Vulcanite 183 

CHAPTER  VII 

Principles  of  Retention  of  Artificial  Dentures   .     272 

CHAPTER  VIII 

Porcelain  Teeth '^^^ 

CHAPTER  IX 
Double  Vulcanization  Method  ....     328 


viii  CONTENTS 


CHAPTER  X 

Aluminum  Base-plate 339 

CHAPTER  XI 

Gold  as  a  Base-plate 364 

CHAPTER  XII 

Tin  as  a  Base-plate 413 

CHAPTER  XIII 
Continuous  Gum  Dentures  .416 

CHAPTER  XIV 

Interdental  Splints 431 

CHAPTER  XV 

Cleft  Palate  Appliances 436 

CHAPTER  XVI 

Esthetics 454 


PROSTHETIC  DENTISTRY 


CHAPTER     I 

THE   MOUTH 

The  mouth,  from  an  anatomical  point  of  view,  is  the 
entrance  to  the  ahmentary  canal;  and  primarily  is  for  re- 
ceiving and  preparing  the  food  for  deglutition.  In  mankind 
there  is  a  secondary  use,  that  is,  to  aid  in  speech  and  expres- 
sion. In  this  chapter  the  mouth  will  be  considered  only  in  its 
primary  relationship;  its  secondary  function  will  be  treated 
in  the  chapter  on  esthetics. 

ANATOMYi 

The  face  is  divided  into  three  portions,  known  as  the  first 
portion  or  upper  third,  second  portion  or  middle  third,  and 
third  portion  or  lower  third  (Fig.  1).  These  thirds  are  indi- 
cated by  four  imaginary  and  approximately  parallel  lines— 
the  first  at  the  top  of  the  forehead,  or  normal  hair  line;  the 

'  It  is  not  within  tlu-  province  of  tliis  monograph  (o  treat  in  detail  either  general  or 
dental  anatomy;  it  considers  onlv  their  practical  application.  It  is  assumed  that  the 
student  has  some  knowledge  of  the  tissues  and  organs  under  consideration;  and  it 
if  hoped  that  the  practically  applied  anatomical  science  will  create  a  desire  for  an 
intimate  acquaintance  with  the  subject. 

For  convenience  of  expression,  the  singular  form  of  the  names  of  bones  and  muscles 
is  used,  although,  with  few  exceptions,  they  are  in  pairs.  One  side  of  the  cranium  is 
a  counterpart  of  the  other 

The  student  is  referred  to  his  text-books  on  general  and  dental  anatomy,  and  espe- 
cially to  the  excellent  article,  '"The  Human  Dental  Mechanism:  Its  Structure,  Func- 
tions, and  Relations,"  by  Charles  K.  Turner.  M.D.,  D.D.S.,  in  the  third  edition  of  the 
American  Text-book  of  Prosthetic  Dentistry. 
2 


18 


THE  MOUTH 


second  at  the  junction  of  the  forehead  and  nose,  or  a  hne 
drawn  at  the  lower  border  of  the  crest  of  the  supra-orbital 
ridges;  the  third  at  the  base  of  the  nose  and  extending  from 
the  anterior  spine  of  the  maxilla  to  the  lower  border  of  the 
external   auditory   meatus;   the   fourth   line   at   the   lower 


Upper 
third 


Middle 
third 


Teeth 
plane 


Lower 
third 


Fig.  1 

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"'■^»A.^H 

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J 

^^■Hr  ■  v 

1 

^Bt  .'98^ ' 

1 

i                    

J 

^r^^^yr 

M 

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.  .^^^^^mt 

border  of  the  chin.  In  passing  it  may  be  noted  that  in  the 
ideal  Greek  face  these  thirds  are  of  equal  length,  but  in 
nature  they  vary  greatly.  These  lines,  however,  are  very 
important  in  the  study  of  the  face,  for  they  determine  the 
proportions — whether  or  not  the  face  is  well  balanced. 


ANATOMY 


19 


Plane  of  the  Teeth. — The  third  Hne,  or  the  naso-auditory- 
meatiis  hne,  is  of  importance  in  marking  or  indicatmg  the 
plane  of  the  upper  twelve  anterior  teeth  (Figs.  1  and  2). 
It  should  be  noticed  that  the  teeth  plane  is  a  straight 
plane  extending  from  the  mesial  angle  of  the  upper  central 
incisor  to  the  distobuccal  cusp  of  the  first  molar;  also  that 


Fig.  2 


the  teeth  plane  indicates  approximatelj'  one-third  of  the  dis- 
tance from  the  third  to  the  fourth  face  line.  The  te(;th  plane 
may  be  extended  backward  and  it  will  be  seen  that  the  second 
and  third  molars  are  progressively  stepped  upward.  Atten- 
tion has  but  re(;ently  been  called  to  this  fact,  so,  to  satisfy 
himself  of  the  truth  of  the  statement,  the  student  should 
not  only  notice  the  few  illustrations  given   (Figs.  1  to  H), 


20 


THE  MOUTH 


but  he  should  observe  every  normal  or  nearly  normal  skull 
and  plaster  cast  of  teeth  that  opportunity  may  present.  The 
straight  line  from  the  crest  of  the  cusp  of  the  upper  cuspid 
tooth  to  the  crest  of  the  distobuccal  cusp  of  the  first  molar 
is  assumed  by  the  author  to  be  the  foundation  of  the  forma- 
ation  of  the  dental  arch;  and  the  other  teeth  in  the  arch  are 
in  compensating  positions.      The  four  teeth — cuspid,  first 


Fig.  3 


Fig.  4 


and  second  bicuspids,  and  first  molar — of  an  artificial  denture 
may  always  be  placed  in  this  straight  line  and  be  considered 
anatomically  normal  and  mechanically  correct. 
^  There  is  a  reason  for  these  four  teeth  being  in  a  straight 
line  and  considered  as  the  foundation  of  the  dental  arch.  By 
referring  to  Fig.  1  it  will  be  seen  that  the  portion  of  the  max- 
illa in  which  these  four  teeth  are  located  has  a  massive 
cubical  block  formation,  and  that  the  remaining  teeth  are 


ANATOMY 


21 


in  extensions  of  this  cubical  block.  The  cubical  block  is 
outlined  by  the  frontonasal  column  A  B,  the  zygomatic 
column  CGD,  the  infra-orbital  arch  BFD,  and  the  molar 
arch  A  C.  The  incisors  are  in  the  lower  nasal  arch  A  E,  a 
forward  extension  of  the  cubical  block;  and  the  second  and 
third  molars  are  in  a  tuberosity  extending  backward  from 
the  cubical  block.  (A  cube  has  the  strongest  formation 
and  the  greatest  resistance  to  force  because  its  dimensions 


Fig.  5 


Fig.  6 


are  equal  in  each  direction.)  This  formation  is  suggestive 
that  the  force  of  mastication  should  be  upon  the  area  of  this 
cube,  and  that  the  straight  formation  has  the  greatest  resist- 
ance to  a  displacing  force  applied  to  an  artificial  denture. 

The  scheme  presented  in  this  book  for  antagonizing  com- 
plete dentures  is  based  upon  this  fundamental  principle. 

Curve  of  Spee. — The  curves  of  Spee  and  of  compensation 
should  be  located  and  thoroughly  established.  The  curve 
of  Spee  is  an  imaginary  one,  and  is  described  as  a  segment  of 


22 


THE  MOUTH 


a  circle  which  begins  with  the  incisal  edges  of  the  lower 
incisors,  passes  over  the  crest  of  the  buccal  cusps  of  the 
lower  bicuspids  and  molars,  and>ends  in  the  anterior  border 
of  the  condyloid  process  (Fig.  7^).  The  degree  of  curvature 
of  this  curve  of  Spec  will  depend  upon  the  angle  of  inclination 
of  the  eminentia  articularis  (Fig.  2,  G).  For  some  years 
writers  and  teachers  have  made  this  curve  of  Spec  (theo- 
retically) the  fundamental  principle  in  the  anatomical 
arrangement  of  tbe  teeth;  and  a  very  elaborate  and  com- 
plicated system  of  "articulation"  has  been  evolved  from  it. 


Fig.  7 


Compensating  Curve. — This  term  has  been  used  as  synony- 
mous with  the  "Curve  of  Spec."  It  should  not  be  so  used, 
for  the  curve  of  Spee  belongs  entirely  to  the  mandible,  and 
is  anatomical;  while  the  compensating  curve  is  mechanical. 
The  compensating  curve  (as  produced  for  mechanical 
reasons)  is  rarely  ever  found  in  nature;  but  should  always  be 
established  in  complete  artificial  dentures.  The  compen- 
sating curve  is  that  arrangement  of  the  teeth  whereby  the 
so-called  three-point  contact  is  established  between  the 
upper  and  lower  artificial  dentures.     If  this  curve  is  to  be 


'  Fig.  7  from  a  photograph  of  a  specimen  in  the  Wistar  Institute  of  Anatomy. 


ANATOMY  23 

of  any  practical  value,  it  must  be  in  harmony  with  the 
excursions  of  the  condyle.  If  the  articulating  surface  of  the 
eminentia  articularis  is  horizontal,  the  condyle  moves 
straight  forward  in  its  excursions,  and  no  compensating  curve 
to  the  teeth  plane  is  required ;  but  if  this  articulating  surface 
is  oblique,  as  is  usual,  then  the  condyle  must  also  descend 
when  it  moves  forward.  This  creates  a  bent  teeth  plane, 
and,  as  has  been  stated,  must  correspond  with  the  path  of 
the  condyle.  If  a  proper  relationship  should  not  be  estab- 
lished between  the  condyle  path  and  the  teeth  plane,  then 
the  artificial  dentures  will  quite  likely  be  dislodged  whenever 
the  teeth  are  occluded  otherwise  than  in  the  retruded  position. 
The  method  of  obtaining  this  relationship  will  be  presented 
in  another  chapter. 

Temporomandibular  Articulation. — This  is  a  condylar- 
thyroidal  joint,  the  structures  taking  part  in  it  being  the 
glenoid  fossa  of  the  tem])oral  bone  and  the  condyle  of  the 
mandible,  together  with  the  ligaments  and  the  tissues  inter- 
posed between  the  bones. 

The  glenoid  fossa  (Fig.  2,  F)  is  an  oblong  cavity  on  the 
under  surface  of  the  squamous  portion  of  the  temporal  bone, 
its  concavity  being  directed  downward.  It  is  bounded 
antciorly  by  the  eminentia  articularis,  externally  by  the 
middle  root  of  the  zygoma  and  the  auditor^'  process,  and 
posteriorly  by  the  tympanic  plate  of  the  petrous  portion  of 
this  bone.  The  anterior  two-thirds  of  this  fossa  is  smooth, 
and  covered,  in  the  recent  state,  with  a  dense  fibrous  tissue, 
and  receives  the  condyle  of  the  mandible.  Of  the  articular 
portion  of  the  fossa  the  distal  part  is  the  most  concave,  and 
is  also  the  most  elevated.  From  this  point  it  slopes  down- 
ward and  forward  to  the  crest  of  the  eminentia  articularis, 
furnishing  a  surface  over  which  the  condyle  glides  in  the 
forward  excursions  of  the  mandible.  The  shape  of  the  cavity 
varies  with  different  nationalities,  with  different  individuals, 
and  sometimes  with  the  opposite  side  of  the  same  individual. 
The  principal  variations  are,  in  size  and  general  concavity, 
in  correspondence  with  the  shape  of  the  condyle,  in  extent 
of  the  surface  from  the  most  concave  portion  of  the  eminentia 


24 


THE  MOUTH 


articularis,  and  in  the  inclination.  The  outhnes  in  Fig.  8* 
show  the  curve  of  its  cavitj-  obtained  from  skulls  after  the 
method  of  Tomes  and  Dolamore.  The  fossa  alters  fre- 
quently in  old  age;  from  the  pull  of  the  muscles  upon  the 
mandible  in  trying  to  bring  into  occlusion  teeth  that  may  be 
widely  separated  in  location. 


Fig.  8 


Outlines  of  glenoid  fossae  obtained  by  the  method  of  Tomes  and  Dolamore.  The 
heavy  base  line  is  parallel  to  a  line  drawn  from  the  anterior  nasal  spine  to  the  fioor  of 
the  external  auditory  meatus.  All  the  fossse  outlines  were  on  the  left  side  of  the  skull: 
A,  from  skulls  with  typical  dentures;  B  and  C,  from  skulls  with  several  teeth  missing; 
D  and  E,  from  edentulous  skulls. 

The  condyle  of  the  mandible  (Fig.  2,  H)  is  the  distal  upper 
extremity  of  the  ramus,  which  fits  into  the  glenoid  fossa. 
The  head  is  an  elongated  oval  body,  with  its  long  axis  at 
nearly  right  angles  to  the  ramus.  The  head  of  the  condyle 
is  separated  from  the  ramus  by  an  elongated  neck,  about 
which  strong  ligaments  are  attached  connecting  the  mandible 
with  the  temporal  bone.  The  head  is  separated  from  the 
glenoid  fossa  by  a  series  of  tissues  that  act  both  as  a  cushion 
and  a  lubricated  gliding  surface.     By  this  peculiar  forma- 


^  Turner's  American  Text-book. 


ANATOMY  25 

tion  various  movements  are  made  possible.  The  mandible 
may  be  carried  bodily  forward  by  unison  in  the  movement 
of  the  condyle  upon  either  side  of  the  cranium.  Whether 
this  movement  is  horizontal  or  oblique  will  depend  upon 
the  formation  of  the  eminentia  articularis.  If  one  condyle 
only  is  moved  forward  the  other  will  rotate  upon  its  axis, 
showing  the  ball-and-socket  formation.  There  is  no  distal 
movement  of  the  head  of  the  condyle,  except  the  slight 
amount  that  may  be  produced  by  compressing  the  soft  tissues 
covering  the  head  of  the  ramus.  It  is  the  action  of  the 
powerful  muscles  of  mastication  upon  either  one  or  both  of 
the  cushioned  condyles  that  makes  it  impossible  to  absolutely 
reproduce  the  movements  of  the  mandible  upon  a  mechanical 
frame.  However,  the  latest  articulators  are  so  scientifically 
designed  that  most  excellent  results  may  be  secured. 

The  Mandible. — This  is  the  preferred  name  for  the  lower  jaw 
(Fig.  2,  J).  It  is  often  called  the  inferior  maxilla,  but  this 
name  is  becoming  obsolete.  The  mandible  is  the  largest  and 
strongest  bone  of  the  face,  and  serves  for  the  reception  of 
the  lower  teeth.  It  consists  of  a  curved  horizontal  portion, 
the  body  (Fig.  2,  J),  and  two  perpendicular  portions,the  rami 
(Fig.  2,1),  which  join  the  back  part  of  the  body  at  nearly 
right  angles.  The  mandible  is  the  movable  arm  of  the  dental 
armament,  therefore  it  is  of  special  interest  to  the  dental 
student,  because  of  its  use  and  the  changes  that  take  place 
with  the  loss  of  the  teeth  and  with  old  age.  Because  of  its 
position  it  is  subject  to  serious  accidents  and  disease, 
namely,  luxations,  fractures,  and  necrosis.  The  large 
muscles  of  mastication  are  principally  attached  to  the  rami, 
and  as  the  condylar  articulation  is  the  only  attachment 
of  this  bone  with  the  cranium,  it  represents  a  lever  of  the 
third  class.  (In  the  third  class  the  power  is  between  the 
fulcrum  and  work.)  While  this  form  of  the  lever  has  the 
least  power,  it  admits  of  the  greatest  latitude  of  movement 
in  the  mandible,  and  demands  the  long  and  strong  muscles 
of  mastication.  The  length  of  the  muscles  is  necessary  to 
permit  freedom  of  movement,  and  their  great  strength  to 
make  possible  the  easy  performance  of  the  work  for  which 


26  THE  MOUTH 

they  are  designed.  That  much  power  is  necessary  for  mas- 
ticating food  can  easily  be  surmised  by  observing  the  power- 
ful grip  of  those  animals  whose  dental  armament  is  not 
designed  for  offence  and  defence.  This  is  well  illustrated  in 
the  horse,  whose  small  mouth  opening  prevents  the  grasping 
of  objects  between  the  molar  teeth;  but  with  its  incisors  it 
may,  in  a  fit  of  rage,  grip  and  shake  a  large  man  or  an  animal 
weighing  two  or  three  hundred  pounds,  as  a  small  terrier 
would  a  rat.  The  power  required  for  man  to  masticate  his 
food  has  been  experimentally  measured  by  both  Professor 
Black  and  Dr.  Head.  Professor  Black  found  that  some 
articles  of  food  require  from  fort}^  to  eighty  pounds  of  force 
to  crush  them,  while  the  highest  figure  obtained  by  Dr. 
Head  was  forty-three  pounds. 

Muscles. — Muscles  are  bands  or  bundles  of  contracting 
fibers  with  two  or  more  attachments.  At  least  one  of  these 
attachments  may  be  considered  as  fixed  or  stationary.  The 
function  of  a  muscle  is  to  produce  motion.  The  motion  is 
produced  by  the  contracting  fibers  drawing  its  movable 
attachment  toward  its  fixation.  As  the  direction  of  the 
force  of  a  muscle  is  always  between  its  attachments,  it 
must  have  a  counter,  because  a  muscle  fiber  can  produce 
but  one  action.  Its  power  is  in  its  contraction.  There  is 
no  active  power  in  the  relaxing  of  the  contracted  muscle 
fiber.  There  are  several  groups  of  muscles  attached  to  the 
mandible,  namely,  muscles  of  mastication,  auxiliary  muscles 
of  mastication,  and  muscles  of  expression. 

The  temporal,  masseter,  external  and  internal  pterygoid 
are  classed  as  the  muscles  of  mastication.  They  are  arranged 
in  symmetrical  pairs,  and  usually  operate  simultaneously  in 
the  movements  of  the  mandible,  although  each  is  capable 
of  independent  action.  They  are  all  attached  to  the  rami, 
and  may  be  considered  as  presenting  no  obstruction  to  the 
wearing  of  artificial  dentures.  They  are  the  powerful  ele- 
vators of  the  mandible.  It  is  through  the  various  inclinations 
of  these  muscles,  acting  in  various  combinations,  that  the 
mandible  is  protruded,  retruded,  and  rotated.  The  depres- 
sion of   the   mandible   is  by  a  different   and   a  much  less 


ANATOMY  27 

powerful  set  of  muscles.  The  depressors  of  the  mandible 
are  the  platysma  myoides,  digastric,  mylohyoid,  and  genio- 
hyoid muscles. 

The  auxiliary  muscles  of  mastication  consist  of  the  bucci- 
nator and  the  composite  muscle — the  tongue.  So  far  as  the 
function  of  these  muscles  concern  the  act  of  mastication, 
they  are  auxiliary  to  the  muscles  of  mastication,  and  their 
use  is  to  keep  the  bolus  of  food  between  the  teeth.  The 
buccinator  (bugle  blower)  muscle  should  be  given  careful 
consideration,  because  its  action  is  such  that  it  may  seriously 
interfere  with  the  stability  of  artificial  dentures.  Its  origin 
is  at  the  union  of  the  alveolar  process  with  the  body  of  the 
maxilla.  It  begins  in  the  proximity  of  the  cuspid  (canine) 
fossa  and  extends  backward  to  the  maxillary  tuberosity 
It  is  inserted  in  the  corresj)onding  portion  of  the  mandible, 
or  just  above  the  external  oblique  line.  When  the  teeth  have 
been  lost  and  there  is  excessive  resorption  of  the  alveolar 
processes,  the  attachments  of  this  muscle  may  be  very  close 
to  the  crest  of  these  resorbed  processes.  In  such  a  case  the 
contraction  of  the  muscle  in  placing  the  bolus  of  food  between 
the  teeth  tends  to  dislodge  artificial  dentures,  especiallj' 
if  the  buccal  flanges  of  the  base-plates  are  too  deep.  Some- 
times, through  carelessness  or  at  least  accidents  in  extracting, 
and  through  improper  or  no  after-treatment,  false  attach- 
ments of  the  muscles  are  formed  upon  the  process.  Iliese 
cases  require  that  the  flanges  of  the  base-plate  shall  be  cut 
away  so  as  not  to  impinge,  otherwise  the  false  attachment 
must  be  surgically  removed. 

While  the  function  of  the  tongue,  as  an  auxiliary  masti- 
cating muscle,  is  to  keep  the  bolus  of  food  between  the  teeth, 
there  are  a  few  of  its  component  muscles  that  need  con- 
sideration. The  mylohyoid  is  attached  to  the  whole  length 
of  the  internal  oblique  line,  and  forms  the  floor  of  the  mouth. 
Sometimes,  through  excessive  resorption,  the  attachment 
of  this  muscle  and  the  crest  of  the  alveolar  ridge  are  in  such 
close  proximity  that  there  can  be  almost  no  lingual  flange  to 
the  base-plate  of  an  artificial  denture;  while  with  other  condi- 
tions an  extensive  lingual  flange  may  be  used  advantageously. 


28  THE  MOUTH 

The  geniohyoglossi  are  attached  to  the  genial  tubercles 
upon  either  side  of  the  median  line.  These  muscles  form 
not  only  an  important  part  of  the  tongue,  but  their  genial 
attachment,  in  excessive  resorption  of  the  process,  form  a 
serious  obstacle  to  the  stability  of  a  lower  artificial  denture. 
The  union  of  the  anterior  borders  of  these  muscles,  with  its 
mucous  membrane  covering,  forms  the  frenum  linguae.  In 
no  case  should  an  impingement  of  the  lingual  flange  of  the 
base-plate  upon  the  frenum  be  permitted.  Upon  the  end 
of  the  body  of  the  mandible,  that  is,  at  the  union  of  the  body 
with  the  ramus,  is  found  the  mandibular  attachments  of  the 
superior  constrictor  of  the  pharynx.  This,  and  the  distal 
border  of  the  buccinator  muscle,  in  conjunction  with  the 
tubercle  formed  as  the  result  of  the  resorption  of  the  alveolar 
process,  indicate  the  extent  to  which  a  lower  denture  may  be 
worn  distally.  The  distal  border  of  the  buccinator  not  only 
passes  between  the  maxilla  and  mandible,  but  also  sends 
some  fibers  to  the  pterygomaxillary  ligaments.  It  is  these 
fibers,  with  their  mucous  membrane  covering,  that  form  the 
soft,  cord -like  tissue  extending  posteriorly  from  the  tuber- 
osity of  the  maxilla.  The  upper  base-plate  should  not  im- 
pinge upon  this  tissue,  as  it  may  dislodge  the  artificial 
denture,  and  also  may  become  very  sore. 

The  muscles  attached  to  the  anterior  external  surface  of 
the  mandible,  are  muscles  of  expression.  Their  location 
may  affect  the  retention  of  an  artificial  denture,  therefore 
we  will  now  consider  them  from  this  viewpoint.  Beginning 
on  either  side  of  the  symphysis  and  extending  outward, 
there  are  the  three  muscles,  levator  labii  inferioris,  depres- 
sor labii  inferioris,  and  depressor  anguli  oris.  These  muscles 
arise  at  and  below  the  union  of  the  alveolar  process  with  the 
body  of  the  mandible.  In  excessive  resorption  of  the  process 
these  attachments  are  so  near  the  crest  of  the  alveolar  ridge 
that  very  little  surface  is  afforded  as  a  seat  for  a  base- 
plate. However,  the  base-plate  must  be  so  formed  as  to 
cover  as  large  a  surface  as  possible,  yet  not  be  displaced  by 
the  action  of  these  muscles.  At  the  symphysis  is  the  frenum 
labii  inferioris  formed  by  the  blending  of  a  few  fibers  from 


ANATOMY  29 

each  of  the  levator  ]al)ii  inferioris  and  the  covering  of  mucous 
membrane.  Sometimes  another  frenum  is  formed  just  distal 
to  the  lower  cuspid  eminence.  This  buccal  frenum  should, 
when  existent,  be  provided  for  in  the  periphery  of  the  base- 
plate. 

Muscles  of  the  Maxillae. — There  are  few  muscles  of  the 
maxilla  other  than  the  buccinator  that  interfere  with  the 
retention  of  the  artificial  upper  denture.  The  depressor  alfe 
nasi  and  compressor  naris  have  their  origin  in  the  incisive 
fossa  and  require  attention  not  only  because  of  their  power 
to  displace  the  artificial  denture,  but  because  of  their  influ- 
ence upon  facial  cosmetics.  When  the  alveolar  process  is 
largely  resorbcd  the  attachments  of  these  muscles  are  some- 
times in  close  proximity  to  the  alveolar  crest.  The  tendency 
seems  to  be  for  the  prosthetist  to  pad  out  or  bolster  up  these 
muscles  with  the  idea  of  restoring  the  expression.  By 
studying  the  origin,  insertion,  and  action  of  these  muscles  it 
will  be  seen  that  the  desired  result  cannot  be  obtained.  The 
endeavor  should  be  not  to  exaggerate  the  deformity.  The 
depressor  alee  nasi  has  two  fasciculi,  the  one  going  to  the 
wing  and  septum  of  the  nose  and  the  other  forming  the 
depressor  of  the  upper  lip.  These  few  fibers,  in  conjunction 
with  a  like  portion  from  the  other  depressor  alse  nasi  and  a 
well-marked  fold  of  mucous  membrane,  constitute  the  frenum 
labii  superioris.  When  it  is  recognized  that  the  function 
of  this  muscle  is  to  draw  in  or  depress  the  upper  lip  and  the 
tip  of  the  nose;  that  the  receding  process  carries  the  origin 
of  this  muscle  farther  back  than  normal,  it  will  readily  be 
seen  that  any  crowding  upward  of  this  muscle  only  tends 
to  still  further  curl  inward  the  upper  lip  and  the  tip  of  the 
nose.  Therefore,  it  is  necessary  that  the  base-plate  shall  be 
well  cut  away  to  permit  free  play  of  the  frenum;  and  that  the 
flange  of  the  base-plate  passing  over  the  incisive  fossa  shall 
be  well  depressed.  Otherwise  there  will  be  a  pouched-out 
efi'ect  of  the  lip  just  under  the  nose.  The  buccal  frenum  over 
the  upper  first  bicuspid  must  not  be  impinged  upon  by  the 
base-plate. 


30  THE  MOUTH 

The  Soft  Palate. — The  soft  palate  (velum  palati)  is  the 
curtain  between  the  vault  of  the  mouth  and  the  pharynx,  and 
is  composed  of  six  pairs  of  small  muscles,  each  having  one 
of  their  attachments  upon  the  palate  bones.  In  some  cases 
these  muscular  attachments  will  extend  farther  forward  than 
usual,  and  in  such  cases  may  interfere  with  the  retention  of  an 
artificial  denture  if  the  base-plate  encroaches  too  much  upon 
them.  This  same  encroachment  may  not  only  cause  loosen- 
ing of  the  artificial  denture,  but  also  nausea.  However,  the 
base-plate,  for  best  retention,  must  extend  in  every  direction 
as  far  as  the  muscles  will  permit,  because,  other  conditions 
being  equal,  the  retention  of  artificial  dentures  is  in  direct 
ratio  to  the  square  surface  covered. 

The  Teeth. — In  the  human  family  the  teeth  are  the  hard, 
flint-like,  symmetrical  formations  placed  within  the  mouth  for 
the  purpose  of  preparing  the  food  for  deglutition.  They  serve 
also  as  an  aid  in  speech,  but  this  is  a  secondary  function, 
and  an  esthetic  rather  than  an  anatomical  subject. 

It  is  necessary  to  study  the  general  characteristics  of  the 
natural  teeth  that  we  may  have  a  comprehensive  apprecia- 
tion of  the  demands  made  upon  artificial  substitutes. 

As  the  teeth  of  a  skull  are  viewed  in  mass  they  are  seen  to 
be  in  two  parabolic  rows  (Figs.  3  to  6).  The  upper  row  is 
fixed  or  stationary,  while  the  lower  one  is  attached  to  a 
hinged  lever  (mandible),  which  carries  them  into  intimate 
relation  with  the  upper.  As  these  two  rows  of  teeth  are 
held  firmly  together  there  is  seen  to  be  a  method  in  their 
form,  grouping,  and  arrangement.  Proceeding  from  the 
median  line  in  either  direction,  in  the  upper  jaw,  the  first 
tw^o  teeth  present  a  straight  edge,  the  next  three  a  single 
point,  and  the  last  three  two  points  each.  It  is  seen  also 
that  the  upper  teeth  overlap  the  lower,  and  that  the  mass 
of  teeth  viewed  as  a  column  has  the  general  form  of  a  trun- 
cated cone.  The  straight-edged  teeth  are  for  cutting  the 
food,  anc[  are  called  incisors,  central  and  lateral.  The  group 
of  three,  with  one  point  each  exposed  when  the  upper  and 
lower  rows  are  in  occlusion,  will  be  found  to  differ  in  form 
when  the  rows  are  separated   and    they  are  viewed  upon 


ANATOMY 


31 


their  ends  (Figs.  9  and  10).  It  will  be  found  that  the  anterior 
one  only  has  but  one  point  or  cusp,  and  hence  is  called  the 
cuspid.     The  remaining  two  teeth  of  this  group  have  two 


Fig.  9 


Fig.   10 


points,  one  terminating  the  outer  or  l)uc('al  surface,  and  the 
other  terminating  tlie  inner  or  lingual  sui'face.  Tiiese  teeth 
are  called  first  and  second  bicuspid  {bi,  two,  and  cw/.s-y;,  point; 


32  THE  MOUTH 

two-pointed,  bicuspid).  The  remaining  three  teeth  at  the 
end  of  the  parabohc  row  will  be  found,  when  viewed  upon 
their  ends,  to  have  from  three  to  five  points,  usually  four; 
these  teeth  are  called  molars — first,  second,  and  third  molars. 
(Molar  is  from  molaris,  belonging  to  a  mill,  derived  from 
mola,  millstone ;  molo,  grind.)  The  teeth  are,  in  order,  named : 
central  incisor,  lateral  incisor,  cuspid,  first  bicuspid,  second 
bicuspid,  first  molar,  second  molar,  and  third  molar.  The 
names  of  the  teeth  are  preceded  by  adjectives  denoting 
location,  as  right  or  left  and  upper  or  lower.  Thus,  to  indi- 
cate a  certain  tooth,  it  should  be  described  as  right  upper 
central  incisor,  left  lower  first  molar;  that  is,  first  indicate 
the  side  of  the  body,  second  the  jaw,  and  third  the  distinctive 
tooth. 

There  is  another  classification  that,  because  of  its  origin, 
needs  consideration.  The  Basle  Anatomical  Nomenclature 
(BNA)  has  the  highest  endorsement  of  anatomists  and  biol- 
ogists. It  is  in  correct  Latin  and  is  designed  to  do  away 
with  duplicate  anatomical  terms.  To  have  one  definite 
name  for  an  anatomical  object  is  most  desirable;  but  for  a 
body  of  general  students  to  elect  terms  for  the  specialist 
student  is  apt  to  be  quite  unsatisfactory.  The  author  of 
this  book  is  of  the  opinion  that  the  specialist  student  should 
not  acquiesce  until  his  claims  have  been  carefully  con- 
sidered. When  brevity  and  simplicity  are  the  cardinal  points 
of  a  scheme,  it  is  certainly  illogical  to  adopt  the  more  cumber- 
some and  less  significant  classification.  This  is  the  relation 
of  the  BNA  tooth  classification  as  compared  with  the 
tooth  classification  of  the  dental  profession.  The  following 
is  the  BNA  tooth  classification  with  the  English  interpre- 
tation, as  given  by  Dr.  Barker,  in  brackets:  Dentes  incisivi 
(incisor  teeth) ;  dentes  canini  (canine  teeth) ;  dentes  prsemo- 
lares  (premolar  teeth  [0.  T.,  bicuspids]);  dentes  molares 
(molar  teeth);  dens  serotinus  (late  tooth  [O.  T.,  wisdom 
tooth]). 

There  is  no  good  reason  for  placing  the  third  molar  in  a 
class  by  itself,  and  the  term  serotinus  (late)  is  as  obnoxious 
as  the  obsolete  term,  wisdom  tooth.    Premolar  is  no  shorter 


ANATOMY  33 

than  bicuspid,  does  not  describe  the  tooth  as  well,  and  has 
the  disadvantage  of  having  been  used  by  some  writers  to 
indicate  the  deciduous  molars.  Canine  (dog)  has  no  scientific 
significance.  As  both  classifications  will  confront  the  student, 
he  should  know  the  writer's  authority  and  reason  for  each. 
This  book  gives  preference  to  the  former  rather  than  the  latter 
classification. 

Returning  to  our  observation  of  the  teeth  in  the  skull 
(Figs.  9  and  10)  it  is  seen  that  the  upper  central  incisor  is 
wider  than  the  upper  lateral  incisor,  that  the  lower  central 
incisor  is  slightly  narrower  than  the  lower  lateral  incisor, 
and  that  the  upper  incisors  taken  together  are  much  wider 
than  the  lower  incisors.  Dr.  Black  gives  the  average  width 
(in  millimeters)  of  the  crowns  of  the  teeth  as  follows: 

r-     ,     ,■■        /  Upper,  9         ^    ^       ...        f  6  4     ^       .  ,  f  7.6     „.    ^  ,  .         .  ,  f  7.2 

Central  mcisor  ,  .  -a      Lateral  incisor  "i  .  „     Cuspid  i  .  _     First  bicuspid      „  „ 

I  Lower,  oA  t  5.9  (  6.9  ( 6.9 

o         Au-         -A   '  6.8      ^.    ,        ,       r  10.7      „  ,        ,       f    9.2      _  .    ,        ,       f    8.6 

Second  bicuspid  •  First  molar  Second  molar  -  Third  molar  •, 

This  formation  permits  all  of  the  lower  central  incisor 
and  half  of  the  lower  lateral  incisor  to  occlude  with  the  upper 
central  incisor  (Figs.  3  to  6),  the  lower  lateral  incisor  to 
occlude  with  the  upper  central  and  lateral  incisors,  and  the 
lower  cuspid  to  occlude  with  the  upper  lateral  incisor  and 
cuspid.  This  arrangement  continues  throughout  the  line 
of  teeth.  In  other  words,  each  tooth,  excepting  the  lower 
central  incisor  and  upper  third  molar,  occludes  with  two 
teeth.  This  arrangement  necessarily  places  each  tooth  of 
the  lower  row,  excepting  the  central  incisor,  half  of  its  width 
(approximately)  in  advance  of  its  fellow  of  the  upper  row. 
The  fact  just  stated  is  fundamental,  and  should  be  fixed 
in  the  student's  mind  as  a  landmark.  For  emphasis,  the 
proposition  is  restated.  Exceptinr/  the  central  incisor,  each 
lower  tooth  is  apjjroxiivateh/  half  its  tcidth  in  admnce  of  its 
fellov)  in  the  npper  parabolic  curve.  In  arranging  the  teeth 
of  a  complete  artificial  denture  this  interlocking  of  the 
teeth  should  always  be  produced.  The  teeth  should  not 
be  arranged  end  to  end,  but  interlocked  one  against  two. 
3 


34  THE  MOUTH 

Farther  on  the  mechanical  reasons  for  this  interlocking  will 
be  developed. 

Parabolic  Curve. — A  parabola  is  a  section  of  a  cone  cut 
parallel  with  one  of  its  sides.  This  will  form  a  figure  with  a 
half  circle  at  one  end,  a  straight  fine  at  the  other,  and  the 
ends  of  the  half  circle  and  straight  line  joined  by  diverging 
straight  lines.  If  a  skull  with  typically  arranged  teeth  is 
held  in  the  hand  so  as  to  secure  a  direct  view  of  the  morsal 
ends  of  the  upper  teeth,  it  will  be  seen  that  the  teeth 
describe  nearly  a  perfect  parabola  (Fig.  9).  Dr.  Bonwill 
demonstrated  that  the  segment  of  the  circle  described  by 
the  six  anterior  teeth  has  a  radius  equal  to  a  line  drawn  from 
the  mesial  incisal  angle  of  the  central  incisor  to  the  distal 
incisal  angle  of  the  cuspid.  The  student  should  appreciate 
that  to  study  any  subject  pertaining  to  nature  it  is 
necessary  to  have  an  ideal — a  type  as  a  standard  for  com- 
parison. It  is  an  axiom  that  nature  never  exactly  reproduces 
herself,  therefore  science  groups  the  easily  recognized 
modifications  of  the  type  into  classes. 

In  studying  a  large  number  of  human  mouths  it  will  be 
observed  that  in  many  cases  the  segment  of  the  circle  will 
have  somewhat  of  a  square  form,  in  others  it  will  be  somewhat 
V-shaped  (with  apex  to  the  front),  and  in  others  afiattened 
round.  This  type  and  the  three  modifications  will  be  further 
considered  in  the  chapter  on  Esthetics,  under  the  heading 
Temperaments.  When  the  teeth  are  all  in  situ  the  radius  of 
the  circle  may  be  easily  obtained  with  a  pair  of  dividers,  but 
when  the  maxilla  is  edentulous  it  is  another  proposition. 
The  next  observation  is  to  determine  how  to  secure  this 
radius  in  an  edentulous  subject.  Upon  the  skull  may  be 
observed  an  elevated  ridge,  cuspid  (canine)  eminence,  over 
the  root  of  the  cuspid  tooth.  This  eminence  terminates 
just  external  to  the  outer  corner  of  the  anterior  nares.  The 
student  may  place  his  finger  upon  his  own  lip  over  the  cuspid 
eminence  and  it  may  easily  be  felt.  By  moving  the  finger 
upward  it  will  be  found  that  this  crest  terminates  within 
the  triangle  formed  by  the  upper  border  of  the  lip,  the  wing 
of  the  nose,  and  the  hnea  nasolabialis.     This  point  indi- 


ANATOMY  35 

cates  the  termination  of  the  influence  of  the  ciisi)i(l  root. 
Thus,  a  point  of  the  di\'iflers  placed  at  the  centre  of  the  base  of 
this  triangle  and  the  other  point  of  the  instrument  placed 
in  the  median  line  just  below  the  crest  of  the  anterior  nasal 
spine  will  indicate  the  length  of  space  to  be  occupied  by  the 
central,  lateral,  and  mesial  half  of  the  cuspid  tooth.  With 
the  dividers  so  set,  and  teeth  selected  to  conform  with  the 
space  indicated,  the  radius  of  the  required  circle  can  be 
obtained  by  extending  the  dividers  to  cover  the  distal  angle 
of  the  cuspid.  In  practice  it  is  unnecessary  to  use  the  instru- 
ment for  this  purpose,  for  the  wax  occlusion  model  should 
be  so  constructed  that  the  cuspid  eminence  is  established 
by  the  mouth.  The  student  should  remember  that  this 
cuspid  eminence  entirely  disappears  with  the  resorption  of 
the  alveolar  process;  so  that  the  labio-naso-buccal  triangle  is 
his  one  guide  in  determining  the  width  of  the  anterior  teeth; 
also  the  radius  of  the  dental  circle.  (Some  operators  con- 
sider that  the  angle  of  the  mouth  indicates  the  distance  to 
which  the  anterior  teeth  should  extend.  This  is,  however, 
a  very  unreliable  guide  by  which  to  determine  the  width  of  the 
anterior  teeth,  because  of  its  instability  and  the  seeming  lack 
of  uniform  conformity  between  the  slit  of  the  mouth  and  the 
other  features  of  the  face.)  The  prosthetist  should  estab- 
lish a  mental  vision  of  the  segment  of  the  circle  described  by 
the  anterior  teeth  and  use  it  as  an  outline  from  which  to 
arrange  the  artificial  teeth  in  each  individual  case.  He 
should  also  keep  in  mind  the  parallelogram  described  by  the 
suture  of  the  maxilhe  and  the  cuspid  eminence.  By  continu- 
ing the  segment  of  the  dental  circle  it  is  seen  that  the  line  not 
only  passes  along  the  incisal  edge  of  the  incisors  and  cusp  of 
the  cuspid,  l)ut  also  through  the  buccal  cusp  of  the  first  bicus- 
pid; and  then  oblicjuely  across  the  sulcus  of  the  second  bicus- 
pid, and  across  the  mesiolingual  cusp  of  the  first  molar  (Fig.  9). 
In  viewing  the  morsal  surface  of  the  upper  denture,  it  will 
be  seen  that  if  a  straight  line  is  drawn  from  the  summit  of 
the  cusp  of  the  cuspid  to  the  summit  of  the  distobuccal 
cusp  of  the  second  molar,  the  line  will  fall  across  all  of 
the  intervening  buccal  cusps.     The  third  molar  is  usually 


36  THE  MOUTH 

deflected  either  lingually  or  buccally  from  the  buccal  cusp 
line.  This  buccal  cusp  line  always  diverges,  to  a  greater  or 
less  extent,  from  the  median  line  of  the  skull.  A  view 
should  now  be  taken  of  the  side  elevation  of  the  skull,  and  it 
will  be  seen  that  the  teeth  plane  is  identical  with  the  diverging 
cusp  line.  Again,  attention  is  called  to  the  short  compen- 
sating curve  formed  only  by  the  elevation  of  the  second  and 
third  molars.  (Other  writers  describe  a  longer  compensating 
curve  which  includes  the  elevation  of  the  distal  cusp  of  the 
first  molar,  and  often  of  the  entire  tooth.)  Dr.  Bonwill  and 
his  successors  have  erred  in  considering  the  curve  of  Spee 
and  the  compensating  curve  equivalent  one  to  the  other. 
Unfortunately,  Dr.  Bonwill  did  not  recognize  the  variable 
condyle  path,  therefore  he  could  combine  his  excellent 
mechanical  invention  of  the  so-called  three-point  contact 
with  the  anatomical  symmetrical  increase  of  the  length  of  the 
cusps  and  overlap  of  the  incisors.  This  he  could  not  have 
accomplished  with  any  other  than  the  horizontal  condyle 
path  without  placing  the  molars  at  such  an  inclination  that 
it  would  seriously  interfere  with  the  retention  of  an  artificial 
denture.  In  Dr.  Bonwill's  "anatomical  articulation"  the 
fatal  error  was  made  not  only  in  failing  to  recognize  these 
two  important  factors,  but  in  endeavoring  to  reproduce  the 
ideal  anatomical  formation  in  place  of  adapting  the  changed 
anatomical  conditions  to  the  laws  of  physics.  In  contra- 
distinction to  the  "anatomical  articulation"  of  artificial 
dentures  we  shall  later  present  the  mechanico-anatomical 
antagonization  of  artificial  dentures. 

Truncated  Cone. — In  viewing  the  occluded  teeth,  as  a  mass, 
it  will  be  seen  that  they  present  the  form  of  a  truncated  cone. 
This  is  necessarily  so  because  the  crest  of  the  alveolar  process 
of  the  mandible  describes  a  larger  circle  than  the  crest  of  the 
alveolar  process  of  the  maxillse.  This  arrangement  favors 
concentrating  the  bolus  of  food,  by  giving  a  lateral  incli- 
nation to  the  grinding  teeth,  the  lowers  being  inclined  inward 
(Fig.  IT)  and  the  uppers  being  inclined  outward.    Usually 

1  Fig.  11  from  photograph  of  a  specimen  in  the  Wistar  Institute  of  Anatomy. 


ANATOMY  37 

the  incisors,  both  upper  and  lower,  inchne  somewhat  outward. 
In  some  cases  the  lower  incisors  incline  inward,  and  in  a  few 
instances  the  upper  incisors  incline  inward,  giving  a  snake- 
like appearance  to  the  mouth.  It  is  quite  probable  that 
this  unsightly  appearance  is  the  result  of  the  unfortunate 
loss  of  the  permanent  first  molars  in  youth.  Too  often  the 
dentist  gives  this  unnatural  inclination  to  artificial  dentures. 
It  is  rarely,  if  ever,  justifiable. 

Fig.  n 


There  is  usually  an  inclination  of  all  the  teeth  toward  the 
median  line  of  the  skull.  This  is  partly  due  to  the  conforma- 
tion of  the  individual  tooth  and  partly  to  the  tilting  of  the 
teeth  bodily  in  that  direction.  As  age  and  especially  as 
certain  diseased  conditions  progress  does  this  mesial  inclina- 
tion prevail. 

Eruption  of  the  Teeth. — Nature  seems  to  have  an  admi- 
rably adapted  plan  for  the  erupting  of  the  permanent  teeth. 
This  function  begins  with  the  lower  first  molar,  upon  each  side 
of  the  mandible,  at  about  six  and  one-half  years  of  age.  This 
tooth  erupts  in  the  angle  formed  by  the  body  and  ramus 
of  the  mandible.  It  is  a  wise  provision  of  nature,  as  it  is  the 
most  fixed  portion  of  either  parabolic  curve,  and  becomes 
the  guide  to  the  eruption  and  dcvcloi)ment  of  the  entire 
dental  armament.     It  is  supported  by  the  coronoid  column 


38  THE  MOUTH 

of  the  ramus  and  causes  the  forward  development  of  alveolar 
process.  As  this  tooth  is  in  a  fixed  and  fortified  position,  it 
directs  and  sustains  the  upper  first  molar  through  their  inter- 
locking cusps.  These  two  teeth  upon  each  side  of  the  mouth 
being  established,  the  other  teeth  must  assume  their  normal 
position  and  usefulness  unless  interfered  with  by  abnormal 
conditions.  The  dental  student  cannot  too  early  become 
imbued  with  the  importance  and  necessity  of  preserving 
throughout  life  the  permanent  first  molars.  The  lower  teeth 
are  all  erupted  in  advance  of  their  correspondents  in  the 
upper  dental  curve  (arch).  For  this  reason  some  dentists 
have  argued  that  the  lower  artificial  denture  should  be  set 
up  first,  and  the  upper  arranged  to  the  lower.  This  argu- 
ment is  not  tenable,  because  the  reason  for  the  order  in  which 
nature  places  the  teeth  is  entirely  difi^erent  from  those  con- 
fronting the  dentist.  Nature's  foundation  principle  is  to 
develop  the  jaws,  while  the  dentist  is  required  to  secure 
mechanical  leverage  for  retention  of  the  artificial  substitute. 
As  the  maxillse  act  as  a  fulcrum,  the  upper  teeth  must  be 
properly  and  securely  placed.  The  second  reason  is  cosmetic. 
The  upper  anterior  teeth  have  much  the  larger  part  in 
establishing  the  contour  and  expression,  while  the  arrange- 
ment of  the  lower  teeth  is  little  more  than  mechanical. 

The  Alveolar  Processes, — The  alveolar  processes  are  the 
portions  both  of  the  maxillae  and  mandible  that  support 
the  teeth.  They  develop  with  the  teeth  and  disappear  with 
their  loss.  The  alveolar  processes  are  removed  by  resorp- 
tion. The  process  of  removal  is  quite  active  for  six  months, 
after  which  it  is  much  slower  for  six  to  twelve  months  longer, 
when  it  is  spoken  of  as  a  settled  or  a  permanent  process  upon 
which  an  artificial  denture  may  be  placed  which  is  designed 
to  be  worn  for  a  few  years.  It  is  the  changing  relation  of  the 
processes  of  the  two  jaws  that  makes  the  wearing  of  artificial 
dentures  so  difficult  for  some  people.  If  measurements 
were  to  be  made  of  the  crest  of  the  alveolar  ridges  of  the 
maxillae  and  mandible  soon  after  the  removal  of  the  teeth,  it 
would  be  found  that  the  radius  of  the  summit  curve  would 
be  greater  in  the  mandible  than  in  the  maxillse.     This  is 


ANATOMY  39 

evident  because  of  the  truncated  cone  formation  of  the 
dental  armament.  i\.s  the  long  axis  of  a  cross-section  of  the 
body  of  the  mandible  is  divergent  from  above  downward, 
it  is  apparent  that  the  radius  of  its  summit  curve  must 
increase  with  its  summit  recession.  While  the  radius  of  the 
summit  curve  of  the  mandible  is  constantly  increasing  with 
resorption,  the  radius  of  the  summit  curve  of  the  maxillae  is 
constantly  decreasing,  therefore  increasing  the  difficulties 
inherent  in  wearing  artificial  dentures.  As  the  palatal 
processes  are  the  least  changeable  of  any  portion  of  the 
maxillae,  the  schematic  drawing  (Fig.  12)  will  explain  why 

Fio.  12 


the  crest  of  the  maxillary  process  recedes  so  rapidly  inward 
as  well  as  upward.  The  two  views  of  the  edentulous  skull 
show  the  result  of  resorption  (Figs.  13  and  14').  It  is  cus- 
tomary to  say  that  where  resorption  has  continued  for  twelve 
to  eighteen  months  they  are  in  a  permanent  condition. 
This  is  only  relatively  so,  for  the  processes  may  slowly 
continue  to  resorb  for  many  years,  not  only  until  the  sur- 
faces occupied  by  the  alveolar  processes  are  perfectly  flat, 
but  until  there  is  an  extensive  concavity.  This  is  especially 
true  of  the  mandible.  The  author,  in  his  practice,  has  con- 
structed two  lower  dentures  in  which  a  portion  of  mandibu- 
lar surface  of  the  base-plate  of  the  artificial  denture  was 
convex  to  the  extent  of  nearly  half  a  circle.    This  (condition 

'  P'iK».  13  and  14  from  photograplm  of  a  Bpecimen  in  tlie  collection  of  Dr.  M.  U.  Cryer. 


40 


THE  MOUTH 


does  not  imply  added  difficulties  in  the  retention  of  the 
denture,  but  it  does  imply  decreased  substance  in  the  man- 
dible and  increased  danger  of  fracture. 


Fig.  13 


Fig.  14 


THE   USE  OF  THE  MOUTH  41 


THE  USE  OF  THE  MOUTH 

Mastication. — As  the  first  essential  for  a  man  is  his  life, 
so  the  first  and  most  important  use  of  the  mouth  is  to  pre- 
pare the  materials  of  sustenance  for  deglutition  and  assimila- 
tion. The  teeth  are  most  important  organs  in  this  operation. 
The  incisors  cut  off  morsels  of  food  of  sufficient  size  for  com- 
minuting between  the  grinding  teeth.  The  bicuspids  are 
designed  especially  to  lacerate  fibrous  food,  while  the  molars 
are  designed  to  pulverize  and  triturate  the  food  with  the 
fluids  of  the  mouth.  It  is  the  importance  of  these  organs 
in  preparing  the  food  for  its  onward  movement  that  creates 
the  dental  profession  for  their  preservation,  and  restoration 
when  lost.  The  physiology  of  mastication  is  beyond  the 
scope  of  this  book,  but  its  importance  is  so  great  that  the 
dental  student  should  familiarize  himself  with  the  subject 
to  a  greater  extent,  if  possible,  than  the  medical  student. 
In  fact,  the  dental  student  should  consider  that  he  is  intrusted 
with  the  comfort  and  preservation  of  the  most  vital  organs 
of  the  human  economy.  It  is  a  lamentable  fact  that  the 
profession  has  not  yet  arrived  at  that  stage  of  proficiency  by 
which  the  organs  of  mastication,  in  all  cases,  can  be  pre- 
served for  use  and  comfort;  therefore,  the  dental  prosthetist 
is  necessary  to  provide  a  substitute  for  the  lost  dental 
organs.  The  dentist  should  appreciate  that  this  office  is 
very  important  and  not  one  to  be  thoughtlessly  turned  over 
to  incompetent  hands.  The  student  of  prosthetics  should 
delve  thoroughly  and  earnestly  into  the  art,  science,  and 
esthetics  of  restoration  that  he  may  properly  serve  those 
needing  his  services. 

Speech. — Articulate  speech  is  the  means  by  which  man 
communicates  his  thoughts.  The  sounds  forming  speech 
are  produced  by  air  passing  over  the  vocal  cords  aided  by 
the  resonant  chambers  of  the  chest  and  head.  The  mouth 
with  the  tongue  is  the  most  important  aid  to  the  vocal  cords. 
The  teeth  are  important  factors  of  the  mouth  in  vocalization, 
as  they  give  support  and  shape  to  the  side  walls  (cheeks) 


42  THE  MOUTH 

and  tongue.  When  the  teeth  are  lost,  certain  muscles  must 
be  developed  and  a  greater  effort  is  required  on  the  part  of 
the  speaker.  With  the  loss  of  the  teeth  there  is  a  permanent 
loss  of  certain  qualities  of  resonance  and  clearness  of  enun- 
ciation that  cannot  be  reacquired  by  developing  the  soft 
tissues.  However,  by  the  aid  of  artificial  dentures  the  original 
conditions  can  be  so  nearly  restored  that  a  defect  in  speech 
can  only  be  detected  by  the  trained  ear.  Indeed,  in  some  cases 
of  natural  defects  and  deficiencies  of  the  mouth  great  im- 
provement of  the  speech  may  be  made  possible  by  properly 
constructed  artificial  dentures  and  appliances.  Artificial 
dentures  may  be  an  impediment  to  speech,  by  the  base-plate 
not  conforming  to  the  parts  upon  which  they  are  supposed 
to  rest,  thus  acting  as  an  edge  to  split  the  expelled  air  of 
vocalization;  or  the  artificial  appliance  may  be  so  cumber- 
some that  it  fills  space  required  by  other  factors  of  enunci- 
ation. However,  all  deficiencies  of  speech  observed  in 
people  wearing  artificial  dentures  are  not  due  to  improperly 
constructed  substitutes.  The  personal  equation  is  an 
important  factor.  Thus,  lisping  and  whistling  are  often 
entirely  unnecessary,  being  faulty  conformation  of  the 
tongue.  Where  the  prosthetist  has  satisfied  himself  that 
the  base-plate  is  properly  fitted  and  retained,  and  that  there 
is  no  unnecessary  incumbrance  to  the  movement  of  the 
tongue,  he  should  explain  and  perhaps  demonstrate  to  the 
patient  that  the  defect  in  speech  is  due  to  the  faulty  use 
of  the  tongue.  The  proper  contour  and  conformation  of 
artificial  dentures  will  be  considered  with  the  technique  of 
construction.  The  object  sought  at  this  time  is  to  establish 
the  fact  that  artificial  dentures  are  an  important  factor  in 
both  restoring  and  impeding  speech. 


RESULTS  OF  LOSING  THE  TEETH 

Importance. — The  importance  of  the  teeth  cannot  be  ques- 
tioned. Their  eruption  and  retention  develop  the  lower  third 
of  the  face,  and  have  much  to  do  with  cosmetics.    Thev  are 


RESULTS  OF  LOSING  THE  TEETH  43 

useful  in  the  formation  of  speech  and,  above  all,  they  are 
necessary  in  preparing  the  intake  of  food. 

Results  of  Loss. — The  loss  of  one  or  more  teeth  in  youth  will 
prevent  the  full  development  of  the  face  and  seriously  inter- 
fere with  the  usefulness  of  the  remaining  ones.  The  loss  of 
one  or  more  teeth  in  adult  life  weakens  the  mesiodistal  sup- 
port of  the  dental  armament  and  ex])oses  a  portion  of  the 
gum  to  injury  during  mastication.  The  loss  of  the  entire 
dentures  makes  impossible  the  mastication  of  food.  There 
are  a  few  exceptions  to  this  statement,  as  there  are  cases  in 
which  the  opposing  jaws  may  be  brought  in  contact,  and, 
by  use,  the  gum  tissue  becomes  so  toughened  that  the  food 
can  be  mashed  and  insalivated.  It  is  a  safe  statement  to 
make  that  the  loss  of  all  the  natural  teeth  adds  ten  to  fifteen 
years  to  the  apparent  age  of  the  patient,  and  it  quite  likely 
cuts  off  as  many  years  of  his  natural  life.  It  is  the  province 
of  the  operative  dentist  to  prevent  these  calamities,  and  the 
duty  of  the  prosthetist  to  supply  substitutes  for  the  losses 
sustained  by  accident,  ignorance,  or  necessity. 

The  statement  is  often  made  that  a  patient  can  only  use 
about  one-fourth  as  much  force  with  artificial  dentures 
resting  upon  soft  tissues  as  could  be  used  with  healthful 
natural  teeth.  This  is  probably  true,  but  it  should  not  be 
assumed  that  artificial  dentures  are  only  one-fourth  as  effectual 
as  natural  ones;  because  in  no  case  does  a  patient  anywhere 
near  use  the  maximum  of  his  power  in  preparing  and  masti- 
cating the  food.  However,  there  can  be  no  ciuestion  but 
that  more  time  is  required  to  properly  insalivate  the  food 
with  artificial  substitutes  than  with  healthful  natural  ones; 
and  there  is  undoubtedly  more  temptation  to  bolt  the  fpod. 
The  loss  of  the  natural  teeth  should  be  considered  a  calamity, 
but  in  such  a  misfortune  one  should  be  grateful  for  the 
services  of  the  prosthetist. 

A  word  as  to  the  time  of  removing  the  natural  teeth  and 
replacing  them  with  artifi(;ial  substitutes.  It  should  be 
established  as  a  fact  that  the  removal  of  the  natural  teeth 
at  any  time  is  more  or  less  a  shock  and  a  strain  upon  the 
nervous  system,  and  especially  so  if  the  pt\tient  is  in  an 


44  THE  MOUTH 

exhausted  or  a  debilitated  condition.  Under  such  conditions 
no  more  teeth  should  be  removed  than  is  necessary  to  give 
relief  from  pain  and  remove  danger  of  septic  infection.  The 
dentist  should  be  very  cautious  about  attempting  to  con- 
struct and  insert  artificial  dentures  while  the  patient  is  much 
below  par  in  physical  rigor.  It  is  not  an  uncommon  incident 
for  the  dentist  to  be  told  that  "father  or  mother  must  have 
some  new  teeth,  as  he  or  she  is  failing  rapidly."  In  these 
cases  the  dentist  should  satisfy  himself  that  there  is  a  lack 
of  adaptation  of  the  artificial  dentures  being  worn,  and  that 
the  unsatisfactory  condition  is  not  due  to  a  lack  of  tone  of 
the  tissue,  in  which  latter  extremity  he  cannot  be  succesful. 


EXAMINATION  OF   THE  MOUTH 

Seating  and  Protecting  the  Patient. — The  patient  should 
be  seated  in  a  dentist's  operating  chair,  facing  a  good  light. 
The  chair  should  be  adjusted  to  the  comfort  of  the  patient, 
and  tilted  slightly  backward.  A  napkin  should  be  fastened 
about  the  neck  of  the  patient  as  a  protection  to  his  clothing. 
If,  after  examination,  an  operation  is  to  be  performed  that 
may  soil  the  patient's  clothing,  a  further  suitable  covering 
for  protection  should  be  provided.  The  mouth  mirror  and 
all  instruments  used  about  the  mouth  should  be  scrupulously 
clean. 

Cleansing  the  Hands. — Special  emphasis  is  placed  upon  the 
cleansing  of  the  hands.  Surgical  cleansing  is  not  necessary, 
but  mechanical  cleansing  is  imperative.  It  is  not  sufficient 
that  the  hands  have  been  thoroughly  cleansed  just  before  the 
patient  enters  the  office,  but  the  patient  should  be  conscious 
that  the  hands  have  been  laved  either  just  before  or  just 
after  he  or  she  is  seated  in  the  operating  chair.  The  impression 
produced  is  most  beneficial.  The  attention  given  the  hands  will 
cause  the  patient  to  unconsciously,  perhaps,  conclude  that 
the  instruments  are  not  only  apparently  clean,  but  are 
clean.  The  dentist  should  establish  a  regular  course  of 
procedure.    IIjs  manner  should  be  positive  but  gentle.    These 


EXAMINATION  OF  THE  MOUTH  45 

attentions  and  methods  will  have  much  to  do  with  securing 
the  confidence  of  the  patient. 

Method  of  Examination. — A  mouth  mirror,  an  examining 
point,  a  pair  of  cotton  tweezers,  possibly  a  blunt  probe, 
absorbent  cotton,  a  supply  of  aseptic  mouth  napkins,  and 
a  water  syringe  should  be  accessible.  A  compressed  air 
spray  is  often  convenient,  but  is  not  a  necessity  in  examina- 
tions, for  the  water  syringe  will  take  its  place.  The  operator 
should  stand  at  the  right  and  slightly  back  of  the  patient. 
This  position  will  give  a  good  view  of  the  mouth,  and  the 
person  of  the  operator  will  not  obstruct  the  light.  This 
position  is  advantageous  for  manipulation. 

The  first  glance  should  observe  any  inflammatory  (sore) 
condition  of  the  lips,  and  then  of  the  interior  of  the  mouth, 
when,  if  such  exists,  the  operator  should  endeavor  to  cause 
the  patient  as  little  discomfort  as  possible,  yet  be  thorough. 
Should  there  be  any  suspicion  of  an  infectious  condition, 
the  operator  should  use  every  precaution  to  protect  himself, 
and  after  the  patient  is  dismissed  every  instrument  used 
about  the  patient's  mouth  should  be  sterilized.  (Steriliza- 
tion is  taught  by  another  chair,  however;  when  not  contra- 
indicated,  keeping  the  instruments  submerged  for  thirty 
minutes  in  boiling  water  will  be  very  effectuaL) 

With  the  mouth  mirror  in  the  right  hand  and  the  assistance 
of  the  fingers  of  his  left  hand,  every  portion  of  the  mouth 
cavern  should  be  brought,  in  turn,  under  inspection  and 
investigation.  Should  the  operator  observe  that  there  is 
resistance  on  the  part  of  the  patient,  such  as  moving  the 
head  or  contracting  the  lips,  he  should  instantly  cast  about 
for  an  explanation.  lie  should  satisfy  himself  that  there 
is  no  evidence  of  filth  about  his  hands  or  instruments,  or 
that  he  is  not  unconsciously  pulling  the  patient's  hair, 
pressing  a  cuff'-button  into  the  ear,  handling  the  mouth  in 
an  awkward  manner,  or  causing  unnecessary  pain.  These 
possibilities  of  discomfort  should  in  an  instant  be  detected 
by  thought  and  a  glance.  Having  satisfied  himself  that 
he  is  not  at  fault,  but  that  the  patient  is  fearful  or  over- 
sensitive, he  should  endeavor  to  overcome  these  conditions 


46  THE  MOUTH 

by  his  gentle  manner  and  kindly  speech.  Often  the  simple 
request  to  relax  the  mouth,  expressed  in  a  gentlemanly 
manner,  will  be  all  that  is  necessary.  At  other  times  an 
assurance  that  the  work  in  hand  does  not  necessitate  pain, 
an  explanation  of  what  is  desired,  or  of  the  condition  found, 
will  place  the  patient  at  ease  through  the  confidence  gained. 

What  to  Look  For. — The  things  to  be  observed  in  the 
mouth  are:  Remaining  teeth  and  roots,  shape  of  arches  and 
vault,  size  of  maxillary  and  mandibular  surfaces,  extent 
and  condition  of  the  alveolar  processes,  muscular  attachments 
and  glandular  tissue,  mucous  and  submucous  tissues,  and 
fluids  of  the  mouth.  We  will  consider  each  of  these  in  the 
order  named. 

Teeth  and  Roots. — A  good  rule  for  the  dentist  to  establish 
is:  The  difficulties  of  inserting,  and  often  in  using,  artificial 
teeth  are  in  the  ratio  to  the  number  required.  While  there 
are  many  exceptions  to  this  rule,  it  is  a  safe  one  when  con- 
sidering the  advisability  of  extracting  teeth.  Another  rule 
is:  A  base-plate  should  not  be  placed  over  a  root  unless  the 
root  is  used  as  a  means  for  support  of  the  artificial  denture. 
Unused  roots  are  a  source  of  irritation,  and  usually  add  to 
the  instability  of  the  artificial  denture.  However,  if  the 
root  can  be  placed  in  a  healthful  condition  and  crowned, 
or  used  as  an  attachment  for  the  artificial  appliance,  it  may 
be  very  valuable.  The  advisability  of  retaining  the  cuspid 
roots  as  an  aid  to  expression  is  very  questionable,  unless 
they  are  used  for  the  retention  of  the  artificial  denture.  In 
practice,  when  preparing  the  mouth  for  artificial  dentures, 
the  operator  must  often  determine  whether  he  will  or  will 
not  retain  one  or  more  sound  and  firm  teeth.  In  no  case 
should  such  teeth  be  removed  until  their  usefulness  as  a  means 
of  retaining  the  artificial  ones  has  been  carefully  considered. 
Sometimes  a  single  tooth  is  of  great  value  in  supporting 
an  artificial  denture;  especially  is  this  true  in  the  mandible. 
A  single  tooth  in  the  maxillae  may  be  of  great  value  when  the 
conditions  are  unfavorable  for  the  usual  methods  of  retaining 
full  dentures.  Two  teeth  in  either  the  maxillse  or  mandible, 
if  properly  located,  may  furnish  the  best  possible  means  of 


EXAMINATION  OF   THE  MOUTH  47 

securing  the  artificial  denture.  However,  a  tooth  or  two 
may  be  so  located  that  their  retention  will  be  a  positive 
detriment  to  the  wearing  of  artificial  dentures. 

It  often  happens  that  the  patient  places  much  value  upon 
the  few  remaining  teeth,  either  for  their  use  or  cosmetics. 
If  there  are  two  teeth,  one  in  each  jaw,  opposing  each  other, 
it  is  always  doubtful  wisdom  to  remove  such;  though  they 
may,  as  they  doubtless  will,  interfere  with  the  retention  of 
artificial  dentures.  In  advising  the  patient,  the  dentist  must 
take  into  consideration  that  the  personal  equation  is  an 
important  factor;  that  the  patient  may  be  one  who  will  never 
make  a  success  of  wearing  artificial  teeth.  However,  one 
factor  that  the  patient  should  be  apprised  of  regarding  the 
retention  of  one  or  more  incisors  only  is  that  if  any  move- 
ment of  the  artificial  teeth  occurs,  it  is  made  conspicuous  by 
reason  of  the  stationary  condition  of  the  remaining  ones. 
The  chapter  on  retention  of  artificial  dentures  will  consider 
the  relative  value  of  individual  teeth. 

Arches  and  J^aults. — The  student  should  have  a  clear 
understanding  of  these  terms.  In  common  parlance,  an 
arch  is  an  upright  structure  spanning  an  opening,  but  this 
does  not  apply  to  the  dental  arches.  The  dental  arch  has 
reference  to  the  paralxjlic  curve  only  of  the  teeth.  It  is 
often  erroneously  used  to  designate  the  curve  of  the  roof  of 
the  mouth.  Such  use  either  shows  ignorance  or  carelessness 
in  the  use  of  accepted  dental  terms.  Vault  is  the  term 
used  to  designate  the  roof  of  the  mouth,  the  more  or  less 
curved  span  over  the  tongue.  The  dental  arches  are  the 
curved  lines  described  by  the  teeth  of  both  the  maxillai 
and  mandible,  while  the  vault  is  the  curved  line  extending 
from  side  to  side  of  the  mouth,  over  the  tongue. 

The  shape  of  the  arches  and  vault  will  be  similar  in  any 
given  case.  Thus,  if  the  iipi)er  dental  arch  is  V-sha])ed,  the 
vault  will  tend  toward  the  same  conformation.  This  is 
easily  explainable.  If  in  infancy  and  childhood  some  infiu- 
ence  is  brought  to  bear  ui)on  the  outer  surfaces  of  the 
})ifusijids  and  molars  (that  is,  the  diverging  straight  lines  of 
tlie  jKirabolic  curve),  so  as  to  compress  them,  it  will  also 


48  THE  MOUTH 

force  the  suture  of  the  palatal  processes  of  the  maxillse 
upward,  giving  the  V-shape  to  the  vault.  Any  continuous 
pressure  upon  the  plastic  osseous  structure  of  youth  will 
have  its  beneficial  or  detrimental  effect.  Thus,  the  shape 
of  the  dental  arches  and  vault  are  similar  unless  they  are 
acted  upon  by  two  or  more  opposing  forces.  While  the  shape 
of  the  arches  and  vault  are  supposed  to  harmonize  with  the 
temperament  of  the  individual,  they  may  be  indicative  only 
of  abnormalities.  The  curve  of  the  edentulous  alveolar 
processes  and  the  vault  will  indicate  the  curve  of  the  teeth 
produced  through  nature,  but  that  is  no  assurance  that  the 
natural  teeth  were  in  harmony  with  the  rest  of  the  physical 
organization.  Consequently  the  curves  of  the  alveolar 
processes  and  vault  are  of  much  interest,  both  directly  and 
indirectly,  to  the  prosthetist.  The  work  being  done  by  the 
orthodontists  in  bringing  the  teeth  of  youth  into  occlusion 
is  of  importance  throughout  life.  It  not  only  helps  to  pre- 
serve the  teeth,  at  least  to  make  them  uesful  while  they  are 
retained,  but  it  puts  the  mouth  in  the  best  possible  shape 
for  the  retention  of  complete  artificial  dentures  when  such 
may  be  required.  Some  persons  may  foolishly  have  sound 
natural  teeth  removed  because  of  their  unsightly  irregu- 
larity, and  with  the  intent  of  having  "beautiful"  artificial 
ones  inserted.  If  possible,  before  the  teeth  are  extracted, 
the  patient  should  be  informed  that  the  conditions  of  the 
mouth  accompanying  the  mal-aligned  teeth  may  add  to  the 
difficulties  of  using  artificial  dentures. 

The  maxillary  suture  or  raphe  requires  special  attention. 
This  is  part  of  the  median  line  noticed  in  many  portions  of 
the  body.  Usually  it  is  little  more  than  a  slight  ridge  or  fold 
of  mucosa;  however,  it  may  develop  to  the  extent  of  an 
obstructive  osseous  tumor  the  size  of  a  man's  thumb.  The 
author's  belief  (based  on  experience  only)  is  that  these 
osseous  enlargements  of  the  raphe  are  much  more  common 
in  the  mouths  of  females  than  of  males.  If  possible,  the 
base-plate  should  pass  about  and  not  over  these  excessive 
enlargements;  at  least,  the  pressure  must  be  relieved  the 
entire  length  of  the  base-plate;  that  is,  even  the  posterior 


EXAMIXATION  OF  THE  MOUTH  49 

edge  must  be  relieved.  A  vacuum  chamber  over  any  portion 
of  this  tumorous  surface  is  more  than  useless.  It  only  tends 
to  concentrate  the  pressure  upon  the  remaining  portion  of  the 
tumor  covered.  Dr.  L.  P.  Haskell  states  that  95  per  cent, 
of  all  cases  requiring  artificial  dentures  need  the  pressure  of 
the  base-plate  relieved  over  this  portion  of  the  vault. 

Size  of  the  MaxiUarii  and  Mandibular  Surfaces. — The 
size  of  these  surfaces  is  not  always  in  harmony  with  the 
size  of  the  individual.  Sometimes  a  very  large  maxillae  is 
associated  with  a  small  physical  organization  and  mouth 
orifice;  at  other  times  the  reverse  occurs,  and  occasionally 
one  is  large  and  the  other  small.  These  varying  conditions 
will  influence  the  construction  and  wearing  of  artificial 
dentures.  These  conditions  should  be  well  noted  in  examining 
the  mouth.  The  size  of  the  maxillic  and  mandible  is  an  impor- 
tant factor  in  retaining  artificial  dentures;  other  conditions 
(shape,  soft  tissues,  tone,  and  fluids  of  the  mouth)  being 
equal,  the  amount  of  retention  will  be  in  the  ratio  to  the 
flat  surface  (base-plane)  covered.  In  estimating  the  amount 
of  retention  surface  that  may  be  of  value  in  retaining  a 
base-plate,  only  that  portion  through  which  direct  pressure 
is  brought  to  bear  upon  the  maxillte  or  mandible  should  be 
considered.  In  those  cases  where  the  maxillary  alveolus 
flares  outward  the  crest  of  the  alveolus  should  define  the 
border  of  the  base-plane.  The  buccal  surface  of  this  class 
of  alveolar  process  will  only  serve  to  prevent  lateral  move- 
ment of  the  base-plate  covering  it,  which,  aided  by  the  soft 
tissues,  will  exclude  the  air,  and  thus  be  of  value  in  reten- 
tion. The  diagrams  (Fig.  15)  representing  cross-sections  of 
maxillse  will  make  clear  this  idea.  The  arrow  points  indicate 
the  distance  to  which  direct  pressure  may  be  applied,  and 
the  dotted  lines  indicate  the  relative  base-planes.  As  the 
base-plates  rest  upon  the  soft  tissue,  it  is  obvious  that 
pressure  brought  to  bear  upon  it  in  the  proximity  of  one  arrow 
only  will  be  concentrated,  and  tend  not  only  to  dislodge 
the  base-plate,  but  to  bruise  the  sup[)orting  soft  tissue; 
while  pressure  applied  at  any  point  approaching  the  median 
line  will  be  more  diffused  over  the  base-plate,  and  conse- 
4 


50 


THE  MOUTH 


quently  present  greater  resistance  and  better  retention. 
This  demonstration  shows  that  the  common  statement  that 
a  flat  vault  is  unfavorable  for  retaining  artificial  dentures 
is  not  well  founded.  The  poor  retention  often  observed 
in  such  cases  is  due  to  other  causes  and  often  to  faulty 
technique  only. 

Fig.  15 


Aheolar  Processes. ^An  earlier  section  of  this  chapter  treats 
of  the  applied  anatomy  of  the  alveolar  processes ;  this  section 
will  treat  of  them  as  supports  for  artificial  dentures. 

When  a  number  of  teeth  have  been  recently  extracted,  in 
common  parlance  the  gums  are  spoken  of  as  fresh  gums,  and 
when  resorption  has  taken  place  they  are  called  permanent 
gums.  In  a  few  days  (seven  to  twenty-one)  after  the  teeth 
have  been  extracted  the  gums  will  have  closed  over  the 
alveoli,  but  the  gums  are  not  in  a  condition  to  withstand 
much  pressure,  yet  they  are  in  shape  for  temporary  artificial 
dentures.  No  matter  of  what  material  the  base-plate  is 
constructed,  when  it  has  been  constructed  for  fresh  gums, 
the  artificial  denture  should  be  considered  as  temporary. 
As  the  alveolar  process  recedes  it  ceases  to  properly  support 
the  artificial  denture.  The  denture  may  become  very 
insecure,  and  often  irritates  the  tissues  severely.  During 
this  process  of  resorption  the  base-plate  may  require  refitting 
once  or  twice;  however,  when  the  artificial  denture  has  been 
worn  from  twelve  to  eighteen  months  a  new  one  should  be 
constructed.  This  is  necessary  to  secure  proper  adaptation 
of  the  base-plate  and  for  restoring  the  contour  of  the  soft 
tissues. 


EXAMINATION  OF  THE  MOUTH  51 

As  the  soft  tissues  (after  extraction)  close  over  the  alveoli 
a  very  irregular  surface  may  present,  from  portions  of  the 
process  having  been  sprung  out  of  position,  or  possibly 
fractured  to  the  extent  of  separation.  In  such  mishaps  the 
loose  pieces  should  be  removed  at  the  time  of  extracting 
the  teeth,  or  as  soon  thereafter  as  discovered;  because  the 
detached  portion  will  not  be  resorbed  by  the  physiological 
process,  but  assumes  a  pathological  import.  So  long  as  the 
displaced  portion  of  process  is  vitally  connected  with  the 
bone  structure,  the  physiological  action  will  dispose  of  it. 
^Meanwhile  the  pressure  of  a  base-plate  may  be  a  source  of 
much  irritation,  and  will  necessitate  cutting  away  sufficient 
of  the  base-plate  for  relief. 

A  well-retained  artificial  denture  must  have  its  greatest  bear- 
ing as  near  the  periphery  of  its  enclosed  base-plane  as  possible. 

When  the  process  of  resorption  is  practically  complete, 
several  conditions  may  be  present  that  should  be  observed. 
The  process  may  be  very  prominent,  so  that  the  lip  is  full 
enough,  and  the  absence  of  the  teeth  not  noticeable  when 
the  patient  is  not  speaking.  In  such  a  case,  when  laughing, 
the  edentulous  subject  may  show  from  a  line  to  a  quarter 
of  an  inch  or  more  of  the  natural  gum.  Cases  of  this  kind 
need  no  artificial  gum  to  restore  sunken  lip  and  cheeks. 
Indeed,  they  probably  present,  when  not  speaking,  a  much 
improved  appearance  from  that  possessed  with  the  natural 
teeth.  The  artificial  denture  should  be  constructed  without 
a  gum  portion  as  far  back  as  the  individual  case  shall  require. 
This  may  require  no  artificial  gum  over  the  two  central 
incisors,  the  four  incisors,  the  incisors  and  cuspids,  or,  in 
extreme  cases,  no  gum  portion  may  be  tolerated  anterior 
to  the  first  molars.  The  artificial  teeth  in  these  cases  must 
be  ground  to  set  closely  against  the  gum,  indeed,  press  into 
and  apparently  grow  from  the  gum.  They  may  be  placed 
with  their  labial  surfaces  in  line  with  the  crest  of  the  process, 
or  they  may  be  carried  outward  and  lap  well  over  the  process. 
The  diagrammatic  sketch  (Fig.  10)  illustrates  these  conditions. 
The  vast  majority  of  cases  may  be  classed  as  regular,  and 
present  no  complications. 


52  THE  MOUTH 

The  resorption  may  continue  until  the  process  is  almost 
extinct,  when  it  is  classed  as  flat.  The  methods  of  handling 
these  cases  will  be  discussed  in  technique  methods,  especially 
the  technique  of  impressions. 

The  process  when  receded  may  be  broad  or  narrow.  The 
broad  alveolar  ridge  is  ordinary,  and  the  thin  (knife-edged) 
ridge  is  only  too  common.  They  are  a  constant  source  of 
annoyance.  In  time  the  thin  alveolar  process  disappears, 
leaving  a  pendulous,  flabby  gum.  The  base-plate  should 
not  be  permitted  to  rest  upon  the  sharp  edge. 


Fig.   1 


Sharp  ridges  may  appear,  upon  any  portion  of  the  process, 
especially  upon  the  lingual  aspect  of  the  mandible.  They 
will  not  tolerate  the  pressure  of  a  close-fitting  base-plate. 

Nodules  from  the  size  of  a  millet  seed  to  a  lima  bean,  or 
larger,  may  appear  on  any  portion  of  the  maxillae  or  mandible. 
If  they  are  to  be  covered  with  a  base-plate  the  pressure  must 
be  removed  from  their  entire  extent.  This  can  be  done  with 
one  or  more  layers  of  No.  60  tinfoil. 

Firm  or  pendulous:  The  firm  gum  consisting  of  an  even 
layer  of  soft  tissue  is  the  desirable  condition,  but  the  pendu- 
lous and  spongy  gums  indicate  complications,  and  the  extent 
of  such  complications  must  be  ascertained. 

Muscular  Attachments  and  Glandular  Tissues. — These  may 
be  observed  and  their  obstructiveness  may  be  judged  by 


EXAMINATION  OF  THE  MOUTH  53 

distending  the  cheeks  and  hps  and  having  the  patient  raise 
the  tongue  to  the  roof  of  the  mouth.  The  subhngual  and 
especially  the  submaxillary  glands  may  interfere  with 
obtaining  a  perfect  impression  of  this  portion  of  the  mandible. 
The  submaxillary  gland  ma}'  entirely  cover  the  bicuspid  and 
first  molar  portion  of  the  mandible.  The  impression  must 
be  obtained  of  the  surface  upon  which  the  gland  rests  and  not 
of  the  gland.  The  method  of  doing  this  will  be  considered 
in  the  chapter  on  Impressions.  The  muscles  and  frena 
attached  to  the  maxillse  and  mandible  have  already  been 
considered,  but  on  examining  the  mouth  the  location  of  their 
attachments  and  any  obstruction  they  may  present  should 
be  carefully  observed. 

Mucous  and  Submucous  Tissues. — The  mucous  membrane 
covers  the  entire  surface  of  the  mouth.  It  is  underlaid  with 
more  or  less  submucous  tissue.  The  condition  of  these  tissues 
is  an  important  factor  in  retaining  artificial  dentures,  and 
requires  observation.  While  all  the  preceding  organs  and 
tissues  which  we  have  mentioned  for  investigation  in  examin- 
ing the  mouth  are  inspected  by  vision,  and  in  a  few  instances 
by  touch  (either  finger  or  instrument),  the  tissues  (mucous 
and  submucous)  under  consideration  can  be  determined  only 
by  the  sense  of  touch.  It  will  be  found  that  in  some  mouths 
the  mucous  membrane  is  \'ery  firm  and  tense  over  the  whole 
surface  upon  which  artificial  dentures  may  be  worn;  in  others, 
that  this  membrane  is  largely  underlaid  with  submucous 
tissue  of  more  or  less  thickness.  It  is  this  class  of  cases  that 
afford  the  greatest  retention  provided  other  conditions  are 
favorable,  and  the  submucous  tissue  is  not  excessive.  A 
third  class  consists  of  those  cases  in  which  a  portion  of  the 
surface  is  covered  with  tense  mucous  membrane  and  other 
portions  are  underlaid  with  submucous  tissue.  These  three 
classes  play  an  important  role  in  the  method  of  taking  impres- 
sions, and  the  method  of  securing  the  retention  of  the  base- 
plate.   They  should  be  carefully  examined. 

Fluids.— The  fluids  of  the  mouth  consist  of  a  mixture  of  the 
saliva  and  nnicous  secretion.  They  may  be  in  moderate 
amount,  or  they  may  bt;  excessive;  they  may  be  thin,  or 


54  THE  MOUTH 

thick  and  ropy.  The  thin  watery  fluid  and  in  moderate 
amount  is  the  most  favorable  for  good  retention  of  artificial 
dentures.  When  the  fluid  of  the  mouth  is  excessive  and  strings 
from  the  mouth  as  an  impression  tray  or  an  artificial  denture 
is  removed,  it  may  be  considered  as  an  unfavorable  factor. 
The  thick  secretion  prevents  that  close  adaptation  necessary 
for  the  strongest  retention. 

Recapitulation. — Having  a  definite  knowledge  of  what 
conditions  may  be  found  in  the  mouth,  the  examination  is 
simple  and  expeditious.  Ordinarily  no  record  is  made  of  the 
examination;  however,  much  valuable  information  could  in 
time  be  acquired  if  blanks  were  used  for  systematic  work. 
When  the  prosthetist  examines  the  mouth  he  desires  to  know 
the  conditions  presenting,  so  that  he  may  determine  at  once 
whether  it  is  an  ordinary  or  a  complicated  case.  The  patient 
being  comfortably  seated,  and  facing  good  light,  the  operator 
makes  a  momentary  visual  and  digital  examination.  By 
this  preliminary  examination  he  determines  whether  there  is 
anything  out  of  the  ordinary  that  may  complicate  the  work; 
if  so,  it  must  be  given  careful  consideration.  If  he  sees  no 
complications,  such  as  inflammatory  conditions  (sores),  unde- 
sirable teeth  or  roots,  ill-shaped  arches  or  vault,  disproportion 
between  the  maxillse  and  mandible,  unfavorable  muscle  or 
frena  attachments  or  gland  complication,  and  no  mucous 
and  submucous  tissue  or  fluid  complications,  he  diagnos- 
ticates the  case  as  ordinary  or  simple,  with  success  contingent 
only  upon  his  technique  and  the  personal  equation  of  the 
patient.  The  prosthetist  then  determines  the  kind  of 
restoration  indicated,  whether  a  bridge  or  an  artificial 
denture,  and  the  variety  of  either  desirable  or  permissible. 
If  there  are  complicating  conditions  present,  he  determines 
whether  they  are  corrective  or  not,  and,  if  not,  how  best  to 
overcome  the  difficulty.  Having  a  clear  conception  of  the 
requirements  of  the  case,  the  prosthetist  consults  with  the 
patient,  as  the  involved  expense  may  be  prohibitive.  An 
artificial  denture  supported  upon  a  base-plate  having  been 
determined  upon,  the  next  step  will  be  to  take  a  suitable 
impression. 


CHAPTER    II 

IMPRESSIONS 

Defintion. — An  impression  is  a  negative  likeness  of  an 
object  or  part  taken  in  a  plastic  material,  from  which  a 
cast  or  positive  likeness  may  be  produced. 

Scheme. — When  the  prosthetist  determines  to  construct  a 
base-plate  artificial  denture,  he  at  once  decides  upon  its 
general  form  and  extent  of  surface  to  be  covered  with  the 
base-plate.  He  also  forms  a  tentative  plan  for  retaining  the 
artificial  denture.  This  plan  for  retention  may  be  altered  or 
abandoned,  as  a  result  of  a  future  critical  study  of  the  case; 
nevertheless,  a  definite  scheme  must  be  in  mind  before  taking 
the  impression,  because  an  impression  suitable  for  the  con- 
templated appliance  should  be  obtained.  An  impression 
that  is  most  desirable  for  orthodontia  may  be  entirely  inade- 
quate for  prosthesis;  and  certainly  an  impression  that  is 
desired  by  either  the  orthodontist  or  the  prosthetist  may  be 
distorted  for  the  other.  This  statement  is  made  to  impress 
the  student  with  the  fact  that  an  impression  is  not  necessarily 
an  exact  negative  likeness  of  a  part,  but  it  must  be  perfect 
in  its  suitableness  for  the  work  in  hand.  The  soft  tissue  is 
the  factor  that  creates  the  variableness  in  impressions. 
Rarely  is  an  impression  perfect  for  its  intended  use  unless 
the  soft  tissues  are,  to  a  greater  or  lesser  extent,  distorted; 
nevertheless  this  distortion  must  be  suitable  for  its  intended 
I>urpose.  The  methods  herein  detailed  are  for  base-plate 
work.  However,  there  is  much  in  common,  in  impression 
taking,  for  all  specialists.  The  extent  of  the  impression 
should  be  governed  by  the  kind  of  an  artificial  denture 
required,  whether  a  partial  or  full,  a  saddle,  or  adhesion 
base-plate.  The  impression  should  extend  a  little  farther 
in  every  direction  than  the  contemplated  base-plate;  but  any 


56  IMPRESSIONS 

excessive  extension  causes  unnecessary  discomfort  to  the 
patient,  and  indicates  indifference  or  thoughtlessness  on  the 
part  of  the  prosthetist.  Therefore,  a  definite  scheme  or 
plan  of  procedure  should  be  devised  for  the  case  in  hand,  and 
good  workmanship  requires  that  every  step  shall  be  neatly 
and  accurately  performed.  This  is  a  fundamental  principle 
of  mechanics,  and,  as  a  profession  is  superior  to  a  trade,  the 
prosthetist  should  show  superior  manipulation.  Another 
thought  for  the  young  student  of  dentistry  is  this :  There  is 
no  legerdemain  associated  with  prosthesis,  the  profession 
being  only  an  expression  of  cause  and  effect;  therefore,  it 
behooves  one  to  cultivate  thoughtfulness  and  thoroughness 
in  manipulation. 

MATERIALS 

There  are  two  classes  of  material  used  for  taking  impres- 
sions. First,  those  substances  made  pliable  by  heat  and  that 
harden  on  cooling;  and  second,  materials  made  plastic  with 
water  and  that  harden  by  crystallization.  Wax,  modelling 
compound,  and  gutta-percha  are  the  materials  of  the  first 
class,  while  plaster  of  Paris  is  the  one  material  of  the  second 
class. 

Wax.^ — Wax  is  a  general  term  applied  to  a  solid  fatty  sub- 
stance obtained  from  all  three  of  the  kingdoms  of  matter. 
The  general  properties  of  the  various  substances  called  wax 
may  be  stated  thus:  They  are  solid  or  semisolid  substances; 
are  easily  broken  when  cold,  but  at  a  moderate  warmth  are 
soft  and  pliable,  and  fuse  at  a  temperature  below  212°  F. 
They  have  a  peculiar  glistening  appearance,  are  lighter  than 
water,  are  insoluble  in  that  fluid  and  in  cold  alcohol,  but 
dissolve  readily  in  ether;  they  are  combustible,  burning  with 
an  illuminating  flame,  and  are  non-volatile. 

Beeswax.— Beeswax  is  an  animal  secretion  formed  by 
bees  from  sugar,  and  is  the  material  from  which  the  honey- 
comb is  formed.  It  is  obtained  by  expressing  the  honey  and 
fusing  the  residue  in  water.  In  this  state  it  is  of  a  yellowish 
color  (Cera  flava) .    It  may  be  bleached,  so  as  to  form  white 


MATERIALS  57 

wax  (Cera  alba),  by  being  exposed  in  thin  slices  to  the  action 
of  solar  light.  The  yellow  wax  is  firm,  breaking  with  a  granu- 
lar fracture,  yellowish,  having  an  agreeable  honey-like 
odor;  not  unctuous  to  the  touch;  melts  at  about  175°  F.; 
is  insoluble  in  alcohol,  but  dissolves  in  oil  of  turpentine, 
ether,  and  chloroform.  It  is  of  a  complex  formation,  and  a 
number  of  derivations  are  obtained  from  it.  C48H92O2  is 
considered  as  its  general  composition. 

Vegetable  Wax. — These  waxes  may  be  obtained  from 
several  varieties  of  plants.  They  are  of  no  value  to  the 
dentist. 

Mineral  Wax. — This  is  a  natural  material  known  as 
ozocerite,  and  is  a  waxy  translucent  mixture  of  the  paraffins 
of  coal  formations.  The  paraffins  have  a  chemical  formula 
of  CnH2n+2.  The  natural  mineral  wax  (earth  wax)  may  be 
used,  but  the  manufactured  mineral  wax  (paraffin,  a  by- 
product of  the  distillation  of  coal  and  petroleum)  is  exten- 
sively used  in  the  dental  laboratory.  It  is  used  in  sheet  form 
as  base-plate  wax,  also  combined  with  beeswax. 

Wax  is  softentd  f(jr  use  by  heating  either  in  hot  water  or  a 
flame,  and  kneading  with  the  fingers.  If  the  wax  is  to  be 
softened  in  water,  .small  lumps  should  be  placed  in  a  dish 
containing  a  quart  or  two  of  cold  water,  then  as  the  water  is 
heated  the  heat  will  penetrate  the  wax  and  not  melt  the 
surface  only,  as  would  be  the  case  if  the  lumps  of  wax  were 
placed  in  hot  water.  As  the  wax  softens  it  is  removed  from 
the  water,  dried  upon  a  cloth  and  kneaded  between  the 
fingers  untjl  it  is  smoothly  plastic.  Should  the  softened 
wax  become  too  hard  for  its  intended  use  it  may  be  again 
warmed  in  the  water  or  passed  a  few  times  through  a  smoke- 
less flame.  The  dry  heat  method  of  working  wax  consists 
in  having  the  wax  from  j,r  to  {  inch  thick  and  passing  it 
repeatedly  through  the  Bunsen  flame  and  kneading  between 
the  fingers.  It  is  reheated  and  kneaded  until  it  is  of  the 
proper  plasticity.  Should  it  be  (neriieated  upon  the  surface 
it  will  aj^pear  crumbly,  but  soon  becomes  smoothly  plastic 
h)y  kneading. 

Beeswax  adulterated  with  tallow  may  be  detected  by  the 


58  IMPRESSIONS 

odor  and  greasy  feeling.  Such  wax  is  not  suitable  for  dental 
purposes. 

Wax  may  be  easily  made  into  sheets  of  any  thickness  by 
the  dipping  method.  The  wax  is  melted  over  water  in  a 
double  pan  (that  is,  one  pan  set  in  a  larger  pan  containing 
water,  thus  lessening  the  danger  of  ignition);  when  it  is 
thoroughly  melted  and  any  dirt  it  may  have  contained  has 
settled,  a  flat  quart  bottle  containing  cold  water  is  dipped 
into  it  and  instantly  removed.  When  the  layer  of  wax  upon 
the  surface  of  the  bottle  has  chilled,  it  should  be  slit  upon  the 
sides  and  at  the  edge  of  the  bottom  of  the  bottle,  when  it 
can  be  stripped  from  the  glass.  Sheets  of  varying  thickness 
may  be  made  by  dipping  repeatedly. 

Modelling  Compound.^ — This  material  is  a  composition  of  a 
resinous  gum,  as  copal,  dammar,  kauri,  etc.,  with  stearin  and 
French  chalk,  colored  and  flavored.  A  formula  and  instruc- 
tion for  compounding,  attributed  to  Mr.  E.  Lloyd  Williams, 
of  London,  England,  is  as  follows:  French  chalk.  If  parts; 
kauri,  1  part;  stearin,  1^  parts.  Melt  the  stearin  in  an 
enamelled  pan  and  stir  in  the  gum.  When  these  are 
thoroughly  incorporated  stir  in  the  chalk.  This  material 
will  be  of  a  yellowish-white  color.  It  may  be  colored  with 
carmine  and  flavored  as  desired.  Modelling  compound  is 
much  used  in  taking  impressions,  for  trial  base-plates,  and 
occlusion  and  contour  models. 

Modelling  compound  is  softened  in  water  after  the  manner 
described  as  the  wet  method  for  softening  wax.  The  surface 
of  the  compound,  just  before  placing  in  the  mouth,  should  be 
passed  over  a  flame.  As  the  softened  modelling  compound 
is  liable  to  adhere  to  the  bottom  of  the  pan,  it  is  a  good  plan 
to  place  one  end  of  a  strip  of  white  paper  in  the  pan  for  the 
compound  to  rest  upon.  The  other  end  is  a  convenient 
means  for  withdrawing  the  compound  from  the  hot  water. 

Gutta-percha  {gatah,  gum;  percha,  the  tree  from  which  it  is 
obtained). — The  gum  is  in  many  respects  similar  to  caout- 
chouc. The  former  is  only  slightly  elastic,  while  the  latter 
has  almost  perfect  elasticity.  Gutta-percha  is  the  dried 
milky  juice  of  a  tree,  Isonandra  gutta,  growing  in  the  May- 


MATERIALS  59 

layan  archipelago.  The  material  may  be  had  at  the  dental 
supply  houses  in  sheet  form.  It  is  considerably  used  for 
trial  base-plates,  and  formerly  was  much  used  for  taking 
impressions.  Its  use  for  this  purpose  has  been,  of  late  years, 
superseded  by  modelling  compound,  a  superior  material. 

Plaster  of  Paris.' — Plaster  of  Paris  is  made  from  the  mineral 
called  (/ypsiim.  This  mineral  is  found  in  various  forms,  as 
massive  or  rock  gypsum;  alabaster,  a  pure  white,  fine-grained 
massive  gypsum;  and  selenite,  a  crystalline,  almost  trans- 
parent gypsum.  The  chemical  composition  of  pure  gypsum 
is  CaS04  +  2H2O.  Therefore,  pure  gypsum  is  a  hj'drous 
sulphate  of  lime,  made  up  of  one  molecule  of  calcium  sulphate 
combined  with  two  molecules  of  water.  This,  when  reduced 
to  percentages  of  weight,  corresponds  to  the  following: 

/-,  ,^,    .^    .  r.rT  ^v       '  Lime  sulphate  (CaS04)     79  I  per  cent. 

Gypsum  (Ca;^04+2H20)  =   >  ,„   ,      ,„  _,  „„  ,_  ^ 

(  Water  (H2O)  20.9  per  cent. 

f  Lime  (CaO) 
Lime  sulphate  =,011,      *  •     ■  i    /c.r>  ^ 
I  Sulphur  tnoxide  (b():j) 

Gypsum  is  rarely  found  chemically  pure.  The  usual  im- 
purities are  silica,  alumina,  iron  oxide,  calcium  carbonate, 
and  magnesium  carbonate.  Usually  these  impurities  do  not 
attain  a  volume  of  3  per  cent.,  and  are  often  less  than  1 
per  cent.  Gypsum  is  prepared  for  the  market  by  grinding  and 
burning,  and  mixing  with  accelerators  and  retarders.  The 
{products  of  manufacture  are  designed  for  a  definite  purpose, 
and  cannot  be  interchanged  advantageously.  The  dentist 
should  have  a  general  knowledge  of  the  various  gypsum 
products,  so  as  to  select  his  plasters  intelligently. 

Classification  of  Plaster. — "  A.  Produced  by  incomplete 
dehydration  of  gypsum,  the  calcining  being  carried  on  at  a 
temperature  not  exceeding  400°  V. 

"  1.  Produced  by  the  calcining  of  a  pure  gypsum,  no  foreign 
material  being  added  either  during  or  after  calcining.  Plaster 
of  Paris. 

'  The  authorities  for  this  genera!  sketch  of  plaster  of  Paris  are:  Cements  and 
f'laaters,  by  Edwin  C.  Eckel,  CIO.,  published  by  John  Wiley  &  Sons,  New  York, 
1907;  Calcareous  Cements,  by  Gilbert  U.  Itedgrave  and  Ctiarlcs  .Spackman,  published 
by  Charles  Gri£Bn  &  Co.,  London,  lyO.O. 


60  IMPRESSIONS 

"2.  Produced  by  the  calcining  of  a  gypsum  containing 
certain  natural  impurities,  or  by  the  addition  to  a  calcined 
pure  gypsum  of  certain  materials  which  serve  to  retard  the 
set  of  the  product.    Cement  plaster. 

"  B.  Produced  by  the  complete  dehydration  of  gj^psum, 
the  calcination  being  carried  on  at  a  temperature  exceeding 
400°  F. 

"3.  Produced  by  the  calcination  of  a  pure  gypsum. 
Flooring  plaster. 

"4.  Produced  by  the  calcination,  at  a  red  heat  or  over,  of 
gypsum  to  which  certain  substances  (usuallj^  alum  or  borax) 
have  been  added.     Hard-finish  plaster.'' 

In  the  trade  these  names  are  used  extensively,  but  at  times 
in  a  careless  and  indefinite  fashion.  Calcined  plaster  com- 
monly means  a  burned  plaster  to  which  no  retarder  has  been 
added.  It  may  be  either  plaster  of  Paris  or  cement  plaster. 
Stucco  plaster  is  less  finely  ground  than  plaster  of  Paris,  and 
usually  is  not  made  of  as  pure  a  quality  of  gypsum.  Wall 
plasters  are  made  by  adding  not  only  a  retarder,  but  some 
kind  of  fiber  to  calcined  plaster.  Keene's,  Martin's,  and 
Mack's  cements  are  hard-finish  piasters  variously  treated  with 
such  substances  as  alum,  borax,  borax  and  cream  of  tartar, 
potassium  carbonate,  and  potassium  or  sodium  sulphate. 

Chemistry  of  Gypsum  Burning. — If  pure  crude  gypsum  is 
heated  to  a  temperature  of  more  than  212°  F.  and  less  than 
400°  F.,  a  certain  definite  portion  of  the  water  of  crystalliza- 
tion will  be  driven  off,  and  the  gypsum  thus  partially  dehy- 
drated will  be  plaster  of  Paris.  Plaster  of  Paris  has  the  for- 
mula CaS04  + YH2O,  which  equals  calcium  sulphate  (CaS04), 
93.8  per  cent.,  and  water  (H2O),  6.2  per  cent.  Dehydration 
to  this  extent  can  be  accomplished  at  any  temperature 
between  212°  F.  and  400°  F.,  but  for  economy  of  fuel  and 
time  it  is  usually  carried  on  at  the  highest  allowable  temper- 
ature; and  330°  to  395°  may  be  regarded  as  the  usual  limiting 
temperature  for  plaster  manufacture.  The  highest  grade 
dental  plaster  is  calcined  at  about  261°  F.  About  400°  F. 
is  a  critical  temperature,  for  if  gypsum  be  heated  much  above 
this  it  loses  all  of  its  water  of  crystallization,  becoming  an 


MATERIALS'  61 

anhydrous  sulphate  of  Hme,  and  useless  as  a  normal  plaster. 
Under  certain  conditions,  however,  "dead-burned"  gypsum 
gains  certain  properties,  and  forms  flooring  and  hard-finish 
plasters.  Partially  dehydrated  gypsum  has  the  property  of 
taking  up  the  lost  water  of  crystallization  and  setting  or 
recrystallizing.  If  the  gypsum  is  piu'e  and  unmixed  with 
retarder,  the  setting  of  the  plaster  will  be  complete  in  a 
few  moments,  while  dead-burned  plaster,  as  such,  is  spoken 
of  as  non-setting;  however,  it  does  set,  but  requires  hours 
for  the  initial  set  and  weeks  for  complete  hydration. 

There  are  three  methods  of  calcining  gypsum,  known  as 
the  kettle,  oven,  and  rotary  cylinder  processes.  Formerly 
the  kettle  process  was  most  used  in  America,  while  the  oven 
and  kiln  process  was  largely  in  vogue  in  England.  The 
rotary  cylinder  process  is  an  improved  method  of  recent 
years. 

Grinding  of  Gypsum  Products. — Grinding  is  an  important 
factor  in  the  manufacture  of  gypsum  products.  In  the  kettle 
process  the  rock  is  first  groimd  and  then  roasted,  while  in 
the  oven  and  the  rotary  cylinder  processes  the  rock  is 
broken  into  convenient  size  masses,  roasted,  and  then  groinid. 
The  use  for  which  the  plaster  is  designed  will  determine  its 
fineness.  The  finest  ground  plaster  only  is  suitable  for 
impressions  and  most  dental  work.  Eckels  states  that: 
"A  dust  chamber  located  above  the  rotary  calciner  catches 
the  most  finely  ground  plaster,  which  is  marketed  for  dental 
plaster  and  other  special  purposes." 

The  Theory  for  the  Setting  of  Plaster. — M.  Le  Chatelier  has 
formulated  a  new  theory,  based  upon  the  phenomena  of  super- 
saturation  investigated  by  Marignac.  This  observer  has 
shown  that  the  "Hydrated  calcium  sulphate  with  half  an 
equivalent  of  water,  which  remains  undecomposed  at  a  tem- 
perature of  about  'A]{)°  v.,  dissolves  freely  when  shaken  up 
with  water,  but  that  after  a  short  interval  the  solution 
becomes  turbid.  This  is  due  to  the  formation  of  a  crystal- 
line precipitate  of  the  common  hydrate  with  two  equivalents 
of  water,  which  has  the  formula  of  gyp.-um.  The  solution 
formed  in  the  first  case  is  five  times  as  concentrated  as  that 


62  IMPRESSIONS 

made  from  the  less  completely  hydrated  sulphate.  It  would 
appear  from  this  that  the  most  important  agent  in  the 
accomplishment  of  the  setting  process  is  the  relatively 
soluble  hydrate,  namely,  that  with  a  small  percentage  of 
water.  This  hydrate  is  at  once  dissolved,  and  then  gives 
rise  to  the  formation  of  the  other  hydrate,  with  the  full 
equivalent  of  water.  The  latter  compound  decreases  the 
solubility  of  the  mixture,  and  the  water  becomes  super- 
saturated with  the  CaS042H20  hydrate,  which  crystallizes 
out.  This  process  continues  so  long  as  there  remains  any 
of  the  soluble  hydrate  [2(CaS04)H20]  to  fortify  the  solution. 

"  The  set  of  plaster  is  thus  the  result  of  two  distinct  series 
of  operations,  which  take  place  simultaneously:  First  the 
particles  of  calcium  sulphate  in  the  act  of  hydration  are  dis- 
solved in  the  water  used  to  gauge  them,  and  produce  a  super- 
saturated solution;  the  solution  thus  formed  deposits  crys- 
tals of  the  hydrate  sulphate.  These  crystals  gradually  increase 
in  size,  and  form  a  compact  mass  in  the  same  way  as  do  all 
similar  crystals  deposited  slowly  from  a  saline  solution, 
and  this  process  is  continued  as  long  as  any  of  the  more 
anhydrous  sulphate  remains  available  to  become  dissolved 
and  to  keep  the  solution  supersaturated." 

The  Expansion,  Contraction,  and  Compressibility. — These 
are  three  properties  of  matter,  of  which  little  has  been 
determined  for  dental  plaster  of  Paris.  However,  in  general 
terms,  it  may  be  stated  that  dental  plaster  first  expands 
and  then  contracts.  The  expansion  is  influenced  by  the 
composition  of  the  brand  of  plaster,  also  by  the  manner 
of  manipulation,  hence  the  stress  that  is  placed  upon  the 
brand  and  method  of  manipulation  in  this  book.  All  plasters 
are  subject  to  eventual  contraction.  Several  men  have,  in  a 
crude  way,  demonstrated  the  expansion  and  contraction  in 
dental  plaster,  and  Prof.  Prothero  has  made  some  scientific 
investigation  along  this  line;  but  not  enough  to  arrive  at  a 
definite  conclusion.  Practice  has  demonstrated  the  truth 
of  the  theory  that  dental  plaster  of  Paris  should  be  com- 
bined with  a  definite  quantity  of  water  and  the  crystallizing 
process  interfered  with  as  little  as  possible.  » 


IMPRESSION  TRAYS  '  63 

Compressihiliiy. — Attention  has  but  recently  been  called 
to  this  property.  The  term  is  indifferently  used  by  various 
writers.  Writers  on  calcareous  materials  for  the  building 
trades  use  compression  as  synonymous  with  crushing,  while 
in  dental  literature  it  refers  only  to  their  condensation  in 
confinement,  not  to  breaking  of  the  unconfined  material 
under  pressure.  This  property  of  the  calcareous  materials 
accounts  for  most  of  the  warping  of  vulcanite  dentures,  and 
is  considered  in  Chapter  VI. 


IMPRESSION  TRAYS 

Definition. — A  dentist's  tray  or  cup  used  for  holding  the 
impression  material  while  taking  an  impression  of  the 
mouth  or  teeth.  Tray  is  the  better  term  to  use,  as  it  conveys 
an  idea  of  a  utensil  having  flanges  and  a  capacity  to  hold 
and  carry,  while  cup  conveys  the  idea  of  symmetry  of  form 
with  a  base  on  which  to  stand,  and  holding  capacity.  Trays 
are  made  of  various  materials  and  sizes. 

Tray  Material. — The  materials  of  which  trays  are  made 
are  block  tin  or  alloyed  tin,  cast  and  pressed  aluminum, 
German  silver,  and  porcelain.  Each  material  has  its  advan- 
tages and  disadvantages,  and  for  special  purposes  the  tray 
should  be  constructed  of  the  materials  best  adapted.  While 
porcelain  is  the  most  cleanly  material,  it  is  not  practical 
because  its  form  cannot  be  changed,  and  it  is  easily  broken. 
Block  tin  (or  some  of  its  alloys)  is  most  commonly  used. 
The  trays  made  of  this  material  may  be  readily  changed  in 
form,  by  cutting  and  bending,  which  is  an  essential  property. 

Tray  Nomenclature. — A  tray  has  a  fjodi/  and  a  handle. 
The  body  consists  of  a  floor  and  flaivges,  and  those  designed 
for  the  upper  jaw  have  a  vault  portion.  There  are  two  types 
of  floors — oval,  for  edentulous  jaws,  andyZa^,  for  accommodat- 
ing remaining  teeth.  The  flanges  are  called  outer  and  inner. 
The  outer  flange  has  two  portions,  the  anterior  or  labial, 
and  the  posterior  or  buccal.  The  dividing  line  is  the  prox- 
imity of  the  distal  surface  of  the  cuspid  tooth.    The  inner 


64 


IMPRESSIONS 


flange  is  also  called  the  lingual  flange.  The  surfaces  of  the 
tray  are  named  for  the  surfaces  they  approximate,  as  maxil- 
lary, labial,  buccal,  and  lingual.  (These  terms  are  used  also 
in  base-plate  nomenclature.)  The  term  palatal  surface  is 
used  indiscriminately,  meaning  either  the  maxillary  or  lingual 
surface.    The  term  is  confusing,  and  should  be  avoided. 

The  vault  portion  spans  the  space  described  by  the  curve 
of  the  lingual  flange  of  the  upper  tray. 

The  handle  is  an  extension  from  the  union  of  the  floor 
and  the  anterior  flange.  The  handle  is  designed  to  be  used 
while  carrying  the  tray  into  the  mouth ;  also  for  removing  the 
tray  and  impression  from  the  mouth.  The  handle  should 
never  be  used  for  holding  the  tray  while  the  impression  is 
hardening,  as  it  acts  as  a  lever,  and  it  is  almost  impossible 
to  avoid  enlarging  the  intaglio  of  the  impression. 


Fig.  17 


Fig.  18 


Tray  Forms. — The  form  of  the  tray  should  be  such  as  to 
approximate  the  form  of  the  part  of  which  the  impression 
is  to  be  taken.  This  would  require  a  great  variety  of  trays, 
therefore  it  is  desirable  to  have  the  trays  constructed  of  a 
material  that  can  be  readily  adapted  to  the  individual  case. 
These  changes  are  made  by  cutting  away  the  undesired 
portion,  or  by  bending  in  or  out  the  portion  not  properly 


IMPRESSION  TRAYS 


65 


adjusted;  or  the  desired  form  may  be  obtained  by  adding 
some  plastic  adhesive  material,  such  as  wax  or  modelling 
compound.  This  added  material  should  not  be  considered 
as  a  part  of  the  impression,  but  as  a  part  of  the  tray  only 
as  the  surface  outline  of  the  built-up  tray  would  be  such  as 
a  specially'  constructed  one  should  have.     In  fact,   some 


prosthetists  have  advocated  taking  a  crude  impression  and 
making  a  plaster  cast  from  which  a  tray  is  constructed. 
(Dr.  Bean's  method,  Turner's  American  Text-book.)  This 
tray  would  have  the  advantages  of  requiring  but  a  small 
amount  of  impression  material,  and  of  carrying  it  accu- 
rately into  place.  Such  methods  require  too  much  time 
and  work,  and  do  not  meet  the  requirements  of  really  diffl- 
5 


66 


IMPRESSIONS 


cult  cases.  The  metal  tray  should  approach  equally  all  the 
surfaces  to  be  impressed.  There  should  be  a  space  of  about 
one-eighth  of  an  inch  to  be  occupied  by  the  impression 
material.  This  will  give  sufficient  body  of  material  for 
strength,  and  in  case  of  fracture  of  the  impression,  the 
pieces  are  thick  enough  to  be  readjusted.    The  exception  to 


Fig 


the  one-eighth-inch  rule  is  where  compression  of  the  soft 
tissues  is  required.  In  such  cases  no  stock  tray  could  answer 
the  purpose;  but  a  simple  stock  tray  may  be  reenforced  so  as 
to  perfectly  meet  the  requirement.  It  is  wise  to  reject  all 
fanciful  and  complicated  trays,  depending  entirely  upon  the 
simplest  forms.    The  various  forms  of  stock  trays  are  made 


IMPRESSION  TRAYS 


67 


in  several  sizes.  The  student  or  young  practitioner  should 
select  a  few  sizes  of  each  of  the  primary  forms,  and,  as 
necessity,  requires  extra  sizes,  special  forms  and  duplicates 
may  be  added  to  the  equipment.  The  several  manufacturers 
offer  similar  lines  of  trays,  and  each  may  have  some  special 
and  fanciful  forms,  but  these  should  not  interest  the  student. 

Fig.  21 


For  the  purpose  of  illustration,  the  well-known  S.  S.  W. 
trays  have  l)een  selected.  These  are  made  of  the  best 
quality  of  Britannia  metal,  and  will  meet  all  ordinary 
requintments.  Fig.  17  shows  an  upper  tray  of  the  oval 
floor  type.     There  are  eight  sizes  of  this  type,  numbered 


68 


IMPRESSIONS 


from  1  (largest)  to  8  (smallest).  For  the  first  outfit  sizes  2, 
4,  and  6  will  suffice.  Fig.  18  illustrates  the  lower  trays  of 
this  type.  There  are  seven  sizes,  of  which  1,  3,  and  7  are 
good  selections.  Fig.  19  represents  the  flat  floor  type. 
There  are  five  sizes  for  the  upper  jaw,  numbered  from  12  to 
16.    Nos.  12  and  15  should  be  the  first  selection.    Fig.  20 


Fig.  22 


Fig.  23 


shows  a  lower  tray  of  the  flat-floor  type.  The  largest  and 
smallest  of  the  sizes,  14  and  16,  will  well  complete  the  initial 
collection  of  trays.  While  the  prosthetist  can  adapt  the  ten 
trays  recommended  to  meet  every  requirement  that  may 
be  present,  it  is  well  to  have  some  special  trays.  The  most 
desirable  of  these  are  shown  in  Figs.  21,  22,  and  23.    The 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      69 

first  two  are  designed  for  the  lower  jaw  only,  while  the  last 
one,  because  of  its  swivel  joint,  may  be  used  in  any  part  of  the 
mouth  for  any  small  impression. 


TECHNIQUE  FOR  FULL  UPPER  IMPRESSIONS 


Classification  < 


Normal. 
High  vault. 

Flat  vaults 


Thin  and  tense  tissues. 
Medium  soft  tissues. 
Soft  and  flabby  tissues,  ropy 
secretions. 


Enlarged  raphe. 


Application. — \Ye  will  suppose  we  have  an  edentulous 
patient  in  the  chair.  The  patient's  comfort  having  been 
looked  after  by  adjusting  the  chair,  placing  suitable  pro- 
tection for  the  clothing,  and  with  a  glass  of  water  upon 
the  bracket  table;  the  examination  of  the  mouth  having 
been  made  as  described  in  Chapter  I,  the  case  being  a 
"normal"  one  in  every  respect,  will  indicate  that  plaster 
impressions  are  required.  The  case  being  of  average  size 
will  require  the  oval  floor  tray  No.  4.  The  tray  should  be 
tried  in  the  mouth  to  ascertain  if  any  alteration  is  required. 
As  the  aperture  of  the  mouth  is  less  than  the  width  of  the 
palatal  end  of  the  tray,  it  will  require  suitable  manipulation 
for  its  insertion.  This  is  accomplished  by  the  operator 
standing  erect,  at  the  right  and  a  little  back  of  the  patient; 
the  patient's  chin  .should  be  about  on  a  level  with  the  elbow 
when  the  chair  and  patient's  head  are  each  slightly  tilted 
backward.  The  patient  is  instructed  to  open  the  mouth 
moderately  wide,  when  the  tip  of  the  index  finger  of  the  left 
hand  is  placed  in  the  left  angle  of  the  mouth.  The  tray  is 
grasped  by  its  handle  between  the  thumb  and  first  two 
fingers  of  the  right  hand.  The  anterior  p(jrtion  of  the  right 
buccal  flange  of  the  tray  is  placed  in  the  right  angle  of  the 
mouth,  an<l  while  distending  the  lips  the  tray  is  swung  into 


70 


IMPRESSIONS 


the  oral  cavity.  The  palatal  border  of  the  tray  is  carried 
upward  over  the  tuberosities,  at  the  same  time  the  anterior 
portion  of  the  tray  should  be  depressed  sufficiently  to  permit 
a  view  of  the  relation  of  the  palatal  border  of  the  tray  with 
the  tuberosities  and  vault. 

Adjusting  the  Tray. — Should  the  flanges  be  too  close  to  the 
tuberosities,  they  may  be  bent  outward  by  grasping  the  body 
of  the  tray  in  the  left  hand,  and  the  use  of  a  pair  of  4-  or  5- 

FiG.  24 


inch  smooth-nosed  plyers  in  the  right  hand.  By  the  same 
means  the  flanges  may  be  brought  nearer  to  the  tuberosities. 
Should  the  vault  portion  impinge,  it  may  be  depressed  by 
striking  a  few  times  with  a  horn  mallet.  (See  Metal  Plate- 
work  Implements,  Chapter  XI.) 

Fig.  24  exhibits  a  tray  with  an  extreme  amount  of  bending 
of  the  flanges  outward,  and  the  vault  portion  slightly  de- 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS       71 

pressed.  In  very  flat  mouths  the  base-plane  may  be  very 
broad,  when  it  would  be  desirable  to  have  the  flanges  bent 
outward  rather  than  cut  away. 

The  anterior  flange  should  next  be  inspected.  Should  the 
tray  impinge  upon  the  frenum  labii,  relief  should  be  afi^orded 
by  deepening  the  notch  in  the  tray  by  use  of  a  half-round 
tile,  such  as  is  used  in  vulcanite  work.  The  flange  at  either 
side  of  the  median  notch  may  require  adjusting,  and  often 
should  be  cut  away.  This  flange  should  not  obstruct  free 
manipulation  of  the  impression  material.  It  would  be 
advantageous  if  this  portion  of  all  prosthetic  trays  were 
largely  cut  aw^ay.  The  student  should  keep  this  axiom  in 
mind,  that  it  is  better  to  have  the  flanges  cut  away  too  much 
rather  than  not  enough,  for  they  may  be  easily  reenforced. 

Reenforcing  the  Tray.^This  may  be  done  with  either  wax 
or  modelling  compound.  The  writer  much  prefers  pure 
yellow  beeswax.  This  is  done  by  softening  a  strip  of  wax 
by  the  dry  heat  method  and  making  it  into  a  roll  a  little 
larger  than  the  shaft  of  a  lead  pencil.  The  palatal  border  of 
the  tray  is  slightly  warmed  in  the  flame  and  the  roll  of  soft 
wax  is  formed  upon  the  maxillary  surface,  permitting  the 
ends  of  the  wax  roll  to  extend  around  the  tuberosities. 
This  is  placed  in  the  mouth  and  forced  firmly  to  place.  The 
tray  is  then  removed  from  the  mouth,  the  wax  made  cold, 
and  any  excess  removed  with  a  hot  wax  spatula  or  knife.  As 
has  been  stated,  this  reenforcement  of  w^ax  is  in  no  sense  a 
I)art  of  the  impression,  it  should  be  considered  only  as  an 
integral  part  of  the  tray.  This  peripheral  reenforcement 
serves  a  double  purpose:  first,  it  acts  as  a  dam  to  prevent  the 
soft  plaster  extending  too  far  backward,  and  second,  it  acts 
as  a  compress  to  prevent  the  contraction  of  the  palate  muscles 
drawing  down  or  depressing  the  palatal  portion  of  the 
impression.  Inattention  to  this  portion  of  the  impression 
often  causes  failure  in  the  retention  of  the  denture.  Fig.  25. 
illustrates  the  tray  with  wax  reenforcement  of  the  palatal 
border.  The  reenforcement  may  extend  forward  upon  the 
buccal  flanges  to  include  the  malar  processes,  but  it  should 
not  extend  so  far  forward  as  to  include  the  buccal  frena 


72 


IMPRESSIONS 


However,  if  the  reenforcement  extends  over  the  malar 
process  it  should  be  properly  adjusted.  This  is  done  as 
follows:  When  the  tray  with  the  peripheral  roll  has  been 
forced  into  place,  the  tray  is  supported  by  firm  pressure  of 
the  index  finger  of  the  left  hand  placed  upon  the  centre  of 
the  lingual  surface  of  the  vault  of  the  tray;  when  the  right 

Fig    25 


cheek  is  grasped  and  drawn  downward  by  the  index  finger  and 
thumb  of  the  right  hand,  the  cheek  is  released  and  instantly 
pressure  is  made  with  the  fingers  upon  the  cheek  over  the  wax. 
The  left  index  finger  is  replaced  with  the  right  one,  when  the 
left  cheek  is  manipulated  in  like  manner.  This  illustration 
shows  also  the  frenal  notch  sufficiently  cut  away  to  prevent 
impingement,  and  the  labial  flange  properly  adjusted.    The 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      73 

tray  is  now  prepared  for  the  case  in  hand,  and  could  not  be 
improved  upon  even  if  a  new  metal  tray  were  to  be  made  for 
this  individual  case. 

Changing  the  Position  of  the  Patient. — The  tray  being 
properly  prepared  for  the  impression,  it  is  well  to  change  the 
position  of  the  patient  to  an  upright  position  with  the  head 
slightly  inclined  forward.  This  is  simply  a  precaution  to 
prevent  any  plaster  falling  into  the  throat.  However,  an 
experienced  operator  may  keep  the  patient  in  the  first 
position  for  his  own  convenience,  and  be  justified  in  so  doing 
because  of  his  expertness;  but  not  so  with  the  inexperienced 
operator. 

Mixing  the  Plaster. — One  fluidounce  of  water,  of  the  tem- 
perature of  the  room  or  a  little  warmer,  is  placed  in  a  rubber 
bowl  (Fig.  20)  and  four  or  five  grains  of  salt  (NaCl)  dissolved 

Fig.  26 


in  it.  A  measure  holding  2  fluidounces  should  be  filled  with 
regular  dental  plaster  (French's),  but  not  packed;  this 
plaster  should  be  shaken  or  sifted  into  the  salted  water  and 
gently  agitated  with  the  plaster  spatula  (Fig.  27)  until  it  is 
smoothly  mixed.  The  object  desired  is  to  get  the  plaster 
cement  smoothly  mixed,  free  from  confined  air,  and  in  the 
mouth  as  quickly  as  possible.  1'he  time  required  should 
be  but  a  few  seconds.  If  a  special  impression  plaster  is  used 
in  place  of  PVench's  regular  dental  plaster,  the  salt  will 
probably  not  need  to  be  added,  as  no  doubt  the  manufacturer 


74 


IMPRESSIONS 

Fig   27 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      75 

has  added  an  accelerator.  Some  operators  prefer  the  use  of 
potassium  sulphate  (K2SO4)  in  place  of  common  table  salt 
(XaCl),  but  either  serves  an  excellent  purpose,  the  XaCl 
having  the  more  agreeable  flavor. 

Filling  the  Tray. — The  mixed  plaster  should  be  transferred 
from  the  bowl  to  the  prepared  tray  as  expeditiously  as 
possible.  The  plaster  should  cover  the  entire  maxillary 
surface  of  the  tray,  it  should  be  flush  with  the  palatal  reen- 
forcement  and  piled  up  somewhat  at  the  anterior  vault 
portion. 

Inserting  and  Placing  the  Filled  Tray.— The  filled  tray  should 
be  instantly  inserted  into  the  oral  cavity,  using  the  technique 
previously  described  in  this  chapter.  While  the  thumb  and 
index  finger  support  the  tray,  the  second  finger  should  be 
carried  backward  against  the  vault  of  the  tray.  This  will 
favor  carrying  the  palatal  border  of  the  tray  firmly  into 
place.  While  placing  the  palatal  border  of  the  tray  the  index 
finger  of  the  left  hand  is  slipped  forward  under  the  lip,  which 
is  grasped  between  the  finger  and  thumb,  and  the  lip  dis- 
tended. As  the  palatal  border  of  the  tray  is  held  securely  in 
position,  the  anterior  portion  of  the  tray  is  carried  into  place 
by  a  swinging  upward  movement  of  the  hand.  Instantly  the 
median  portion  of  the  lip,  which  is  in  the  grasp  of  the  finger 
and  thumb  of  the  left  hand,  should  be  drawn  downward,  thus 
settling  the  frenum  labii  in  the  soft  plaster. '  The  finger  is 
then  slipped  backward  to  the  left  angle  of  the  mouth,  which 
is  grasped  and  drawn  downward,  marking  and  placing  the 
buccal  frenum.  Either  the  first  or  second,  or  both  of  these 
fingers  of  the  left  hand  are  placed  against  the  vault  of  the 
tray,  thus  releasing  the  right  hand.  The  right  angle  of  the 
mouth  is  now  drawn  downward,  thus  placing  the  right 
buccal  frenum.  While  firm  pressure  is  maintained  upon  the 
\ault  of  the  tray,  the  cheeks  and  lip  are  firmly  pressed  against 
the  soft  plaster  with  the  thumb  and  fingers  of  the  right  hand. 
By  this  means  the  soft  tissues  of  the  l)uccal  and  labial 
walls  of  the  maxillae  are  compressed.  No  effort  need  be 
made  to  compress  the  plaster  over  the  malar  processes,  as  the 
wax  reenforcement  will  provide  for  this.     Furthermore,  if 


76  IMPRESSIONS 

there  is  any  portion  of  the  periphery  of  the  plate  that  should 
not  press  firmly,  it  is  that  over  the  malar  processes.  The 
fingers  of  the  right  hand  may  now  relieve  the  left  hand,  which 
is  placed  upon  the  top  of  the  patient's  head.  By  pressing 
with  both  hands,  not  hard  but  firmly,  the  setting  plaster  is 
held  more  steadily  in  place.  If  the  operator  removes  a  little 
of  the  excess  plaster  upon  a  finger  of  the  left  hand  as  he 
removes  it  from  the  mouth  the  last  time,  he  will  have  a  guide 
as  to  the  hardening  of  the  plaster.  It  should  be  left  in  the 
mouth  (probably  two  or  three  minutes)  until  it  will  break 
with  a  clean  fracture,  when  it  is  ready  to  be  removed. 

Removing  the  Impression. — When  the  plaster  breaks  with 
a  clean  fracture  and  does  not  crush,  the  impression  should 
be  removed  by  grasping  the  handle  of  the  tray  with  the  thumb 
and  fingers  of  the  right  hand,  while  the  left  cheek  is  elevated 
from  within  with  the  index  finger  of  the  left  hand.  Pressure 
is  made  upon  the  handle  in  such  a  manner  as  to  depress  the 
palatal  border  of  the  impression.  If  the  impression  does 
not  loosen  after  a  reasonable  amount  of  force  has  been 
applied  in  this  manner,  a  slight  rocking  movement  of  the 
handle  up  and  down  may  aid.  If  the  operator  has  left  the 
impression  too  long  in  the  mouth  it  may  be  necessary  to 
throw  a  jet  of  water,  with  a  water  syringe,  around  the 
periphery  of  the  impression.  This  is  done  by  tilting  the 
head  slightly  backward  and  lifting  the  lip  and  cheek  upon 
one  side,  when  the  crevice  between  the  impression  and  the 
lifted  soft  tissues  is  filled  with  water.  The  other  side  of  the 
mouth  is  treated  in  the  same  manner,  when  the  handle  should 
again  be  manipulated.  If  the  impression  is  removed  at  the 
proper  time  there  will  be  only  moderate  adhesion.  Strong 
adhesion  of  a  plaster  impression  is  no  evidence  that  it  is  a 
good  one,  but  it  is  a  positive  evidence  that  the  plaster  has 
been  left  so  long  in  the  mouth  that  it  has  absorbed  all  the 
moisture  from  the  surface  of  the  mucous  membrane,  thus 
creating  a  powerful  vacuum  suction,  which  upon  being 
broken  may  tear  the  mucous  membrane.  With  attention 
given  to  the  work  in  hand  there  should  be  no  excuse  for 
such  an  accident. 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      77 

Fig.  28  shows  tlie  maxillary  surface  of  a  plaster  impression. 
Notice  the  peripheral  outline.     Fig.  29  shows  the  palatal 

Fig.  28 


Fig.  29 


78 


IMPRESSIONS 


border  of  the  impression.  Notice  the  clean  cut-off  of  the 
plaster  by  the  wax  reenforcement.  Fig.  30  is  another 
plaster  impression  in  which  the  palatal  border  reenforcement 
wax  has  entirely  excluded  the  plaster  in  places,  as  can  be 
seen  by  the  difference  in  color.  This  illustration  shows 
also  the  excess  plaster  pressed  forward  upon  the  handle  of 
the  tray.  The  edge  of  the  anterior  flange  of  the  tray  can  be 
seen  much  below  the  periphery  of  the  impression,  and  yet 

Fig.  30 


there  is  much  thickness  to  the  labial  wall  of  plaster.  This 
is  because  the  low  labial  wall  of  the  tray  was  reenforced  with 
wax,  which  with  the  soft  plaster  was  forced  against  the  labia 
wall  of  the  maxillae  by  the  external  pressure  upon  the  lip. 
In  contrast  with  this,  Fig.  28  shows  a  thin  labial  wall  of 
plaster,  because  a  higher  anterior  flange  was  used  with  no 
wax  reenforcement.    Fig.  31  shows  a  tray  with  palatal  and 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      79 

labial    wax    reenforcements    ready    to    receive    the    freshly 
mixed  plaster. 

The  method  detailed  will  suffice  for  a  very  large  percentage 
of  cases  requiring  a  full  upper  artificial  denture;  but  there 
are  some  cases  that  will  recjuire  special  manipulation  in  order 
to  produce  the  best  results.  These  may  be  classified  as: 
(1)  High  vaults,  (2)  flat  vaults,  and  (3)  enlarged  raphe. 

Fig.  31 


High  Vaults. — The  high  vault  may  be  oval,  square,  or  an 
inverted  V-shape.  In  either  case  the  wax  reenforcement 
should  not  only  be  placed  along  the  palatal  border,  but  it 
should  be  carried  forward  to  fill  the  entire  vault.  After 
the  wax  has  cooled,  the  surface  of  the  anterior  portion  to 
the  thickness  of  f ,;  of  an  inch  should  be  removed  with  a 
warmed  wax  knife.    The  palatal  border  should  be  left  undis- 


80 


IMPRESSIONS 


turbed  to  the  width  of  ^  to  f  of  an  inch.  The  object  of  the 
reenforced  vault  portion  is  to  insure  the  plaster  being  carried 
fully  to  place,  and  the  use  of  less  plaster.  Fig.  32  shows  a 
tray  prepared  for  an  inverted  V  vault.  A  high  vault  will 
always  require  a  high  labial  flange  to  the  tray.  It  is  better 
to  use  a  tray  with  a  narrow  labial  flange,  and  then  build  the 


required  flange  of  wax,  thus  providing  for  the  compression  of 
the  soft  tissues  over  the  labial  wall  of  the  maxillse.  The  illus- 
tration shows  the  low  metal  flange  upon  the  right  side  and 
the  wax  restoration  upon  the  left. 

Flat  Vaults. — These  cases  will  present  one  of  three  condi- 
tions of  the  soft  tissues:  (1)  Thin  and  tense;  (2)  medium  soft; 
or  (3)  soft  and  flabby.    Fig.  33  is  a  cast  of  the  second  class, 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      81 

The  impression  from  which  this  cast  was  made  was  taken 
in  the  tray  shown  in  Fig.  24.  Obviously  a  case  of  this  kind 
would  require  that  the  flanges  of  the  tray  should  be  cut  away 
or  that  they  should  be  bent  well  over,  as  shown.  The  latter 
is  to  be  preferred,  as  it  provides  the  desired  large  base  plane. 
(This  feature  will  be  further  considered  under  the  subject 
Retention  of  Artificial  Dentures.)  In  both  the  first  and 
second  classes  the  impression  is  taken  in  the  usual  manner. 
It  is  in  these  flat  cases  that  the  student  is  tempted  to  omit 
the  palatal  border  wax  reenforcement,  but  he  should  remem- 
ber that  the  rule  is  universal,  and  has  no  exceptions,  that  to 
omit  this  reenforcement  in  any  case   is   to  invite  failure ; 


Fig.  33 


however,  failure  may  not  come  at  the  bidding.  The  third 
class  of  flat  vaults  requires  special  consideration  and  treat- 
ment. 

Difficult  Flat  Vaults. — The  flat  vault  per  se  is  not  neces- 
sarily difficult  to  cope  with,  for  under  favorable  conditions 
it  provides  the  strongest  retention.  However,  there  are 
such  a  considerable  number  of  vexatious  cases  associated 
with  flat  vaults  that  they  have  become  the  hete  noire  of  the 
flental  profession.  This  is  a  very  unjust  condemnation, 
because  there  are  other  vault  forms  that  present  much 
greater  difficulties.  The  trouble  is  that  the  dentist  fails  to 
recognize  the  conditions,  therefore  fails  to  meet  the  require- 
6 


82 


IMPRESSIONS 


merits.  In  the  three  classes  named  of  conditions  of  the  soft 
tissues,  the  first  class  (hard  and  tense)  presents  only  the 
usual  difiiculties  of  impression  taking;  yet  the  retention  in 
this  class  is  poor.  This  will  be  considered  in  the  chapter 
on  Retention.  The  second  class  (medium  soft  tissues), 
provided  the  fluids  are  normal,  is  one  of  the  most  favorable 
cases  the  dentist  can  have.  The  third  class  (soft  and  flabby) 
are  troublesome  and  require  study,  and  suitably  taken 
impressions. 

Fig.  34 


Before  entering  upon  the  technique  of  taking  impressions 
for  this  class,  it  is  necessary  to  refer  to  another  factor  some- 
times associated  with  flat  vaults.  A  thick  ropy  secretion  is 
always  a  menace  to  the  retention  of  artificial  dentures.  This 
factor  is  mentioned  at  this  time  because  one  method  of 
impression  taking  is  especially  designed  to  offset  the  viscid 
secretions.  In  this  third  class  the  flabby  tissue  may  be 
evenly  distributed  over  the  entire  surface  to  be  covered  with 
the  base-plate,  or  it  may  be  interspersed  with  hard  tissue. 
Each  condition  will  require  a  suitable  impression. 


TECHNIQUE  FOR  FULL   UPPER  IMPRESSIONS      83 

Technique  for  Flabby  Gum. — ^Yhell  the  soft  tissues  are 
thick  and  evenly  hiid  o\er  the  surface  to  be  covered  with  the 
base-plate,  a  suitable  size  flat  oval  floor  tray  is  selected,  a 
roll  of  soft  wax,  the  size  of  a  lead  pencil,  is  placed  upon  the 
maxillary  surface  at  the  periphery  of  the  tray,  carried  into 
the  mouth,  and  pressed  firmly  into  place.  While  holding 
the  tray  firmly  with  a  finger  or  two  upon  the  centre  of  the 
vault  of  the  tray,  the  lip  and  cheeks  are  drawn  dow^nward  and 
then  externall\-  pressed  inward.  The  tray  is  then  removed 
from  the  mouth,  and  the  wax  cooled.  The  space  formed  by 
the  peripheral  wax  is  filled  with  a  soft  mix  of  plaster.  The 
technique  of  inserting  the  tray  into  the  oral  cavity,  and 
adjusting  it  is  the  same  as  previously  described.  The  object 
sought  is  to  have  the  soft  tissues  evenly  compressed  through- 
out the  entire  periphery  of  the  base-plate  and  no  compres- 
sion over  the  enclosed  portion.  Fig.  34  shows  a  flat  tray  with 
peripheral  wax. 

Technique  for  Interspersed  Hard  and  Soft  Tissues. — As  an 
axiom,  it  may  be  stated  that  increased  pressure  shf)uld  not 
be  placed  upon  either  hard  or  soft  tissue  in  the  vault  of  the 
mouth  except  upon  the  palatal  border;  or,  conversely  stated, 
increased  pressure  should  be  made  upon  the  palatal  border, 
the  alveolar  ridge,  and  external  to  the  alveolar  ridge.  The 
most  common  occurrence  of  the  condition  under  consider- 
ation is  a  spongy  vault  with  the  alveolar  ridge  moderately 
hard  upon  either  side  as  far  forward  as  the  location  of  the  cus- 
pids, and  a  flabby  condition  from  cuspid  to  cuspid  location. 

Fig.  35  is  a  tray  reenforced  for  such  a  case.  The  palatal 
border  wax  should  extend  forward  to  rest  upon  the  malar 
process,  only  when  it  is  covered  with  an  excessive  amount 
of  soft  tissue.  The  anterior  portion  of  the  tray  should  have 
a  sufficient  quantity  of  wax  to  cover  aU  of  the  flabby  gum 
tissue.  The  metal  flange  should  be  cut  low  and  replaced 
with  a  thin  j)iece  of  yellow  wax.  As  in  all  cases,  the  soft  wax 
is  adjusted  to  the  mouth.  The  tray  is  filled  (avoid  much 
excess)  with  moderately  thin  plaster,  inserted,  and  adjusted 
as  previously  described.  Notice!  Hard  (not  firm)  but  hard- 
continued  }>ressurc  is  made  upon  the  centre  of  the  vault  of 


84 


IMPRESSIONS 


the  tray.  The  Hp  and  cheeks  are  drawn  downward  and 
compressed  externally  as  in  other  cases.  The  pressure  upon 
the  tray  is  continued  until  the  plaster  has  set.  By  this 
means  a  firm  foundation  will  be  established  for  the  artificial 
denture. 

Rarely  will  the  buccal  portion  of  the  gum  tissue  be  exces- 
sively flabby,  but  when  it  is  it  must  be  compressed;  and  the 
buccal  flange  of  the  base-plate  must  extend  as  far  outward 


Fig.  3o 


as  the  free  action  of  the  buccinator  muscle  will  permit.  The 
object  sought  is  to  have  the  force  of  mastication  distributed 
over  as  broad  a  surface  as  possible,  and  thus  prevent  undue 
pressure  upon  the  palatal  processes  of  the  maxillae. 

So  far  there  has  been  discussed  but  one  method,  with  its 
modifications,  for  taking  full  upper  impressions.  The  reten- 
tion principle  underlying  this  method  is,  "  Uniform  pressure 
and  absolute  contact."  This  principle  is  more  scientific 
and  less  subject  to  ad^'erse  criticism  than  the  remaining  one 


TECHNIQUE  FOR  FULL    UPPER  IMPRESSIONS      85 

(atmospheric  pressure)  for  retaining  full  up])er  artificial 
dentures.  Plaster  of  Paris  with  a  suitably  prepared  tray  is 
the  best  material  the  dental  profession  of  today  possesses 
to  meet  the  requirements  of  the  cases  so  far  detailed.  The 
one  serious  objection  to  plaster  of  Paris  is  that  there  is  no 
practical  test  for  the  perfection  of  the  impression.  Depen- 
dence must  be  placed  upon  knowledge  and  skill;  knowledge  of 
the  requirements  of  the  case  and  skill  in  applying  the  knowl- 
edge. Should  a  plaster  impression  be  replaced  in  the  mouth, 
strong  adhesion  may  be  induced  by  its  capacity  to  absorb 
the  mositure  upon  the  mucous  membrane;  but  this  will 
take  place  equally  as  well  or  better  with  a  poorly  adapted 
impression.  An  inspection  of  the  impression  may  show  a 
perfect  imprint  of  the  mucous  membrane,  but  it  does  not 
differentiate  between  proper  compression  and  improper 
distortion  of  the  soft  tissues.  So  knowledge  and  applied 
knowledge  (skill)  must  be  arbiters  of  the  perfection  of  the 
impression.  The  artificial  denture  made  from  an  impression 
may  be  positive  evidence  that  the  impression  was  perfect,  but 
it  is  no  evidence  that  it  was  not  good. 

Mention  has  been  made  of  ropy  or  viscid  secretions  as  isn 
adverse  factor  associated  with  flat  and  more  or  less  flabby 
vaults.  The  author  is  of  the  opinion  that  these  conditions 
may  be  best  met  by  the  use  of  modelling  compound.  Also, 
he  believes  that  no  first  impression  should  be  taken  with 
this  material,  because  the  line  of  demarcation  where  plaster 
ceases  to  be  the  best  material  and  modelling  compound 
demanded  is  so  obscure  that  preference  should  always  be 
given  plaster  of  Paris.  Modelling  compound  is  far  more 
difficult  to  handle  Tproperly)  than  plaster  of  Paris.  The  latter 
material  is  more  scientific  and  requires  less  skill  than  the 
former,  especially  if  the  case  is  a  difficult  one.  This  last 
statement  is  contrary  to  the  generally  accepted  opinion,  but 
nevertheless  it  is  true.  The  reasons  for  these  statements  will 
fievelop  as  the  methods  for  the  use  of  the  c(jnii)oun(l  are 
described. 


86  IMPRESSIONS 


MODELLING  COMPOUND  FOR  FULL  UPPER 
IMPRESSIONS 

As  Ordinarily  Used. — A  tray  is  selected,  and  the  flanges 
adjusted  as  for  a  plaster  impression.  No  reenforcement 
is  required.  A  portion  or  a  whole  cake  of  modelling  com- 
pound, as  the  judgment  dictates,  is  softened  in  water  (see 
page  58)  and  placed  in  the  warmed  tray.  In  manipulating 
the  compound  all  folds  should  be  kept  on  the  under  portion, 
so  the  surface  taking  the  imprint  may  be  smooth  and  con- 
tinuous. The  side  of  the  index  finger  may  be  embedded 
first  upon  one  side  and  then  upon  the  other,  so  as  to  form  a 
groove  for  the  alveolar  process.  The  surface  is  then  given 
an  extra  softening  by  passing  over  a  smokeless  flame.  The 
compound  fllled  tray  is  carried  into  the  mouth  and  forced 
into  place  after  the  manner  described  for  plaster  (page 
69).  The  lip  and  cheeks  are  manipulated  in  the  same 
manner  as  for  plaster.  The  compound  is  left  in  the  mouth 
until  it  has  hardened.  Hardening  may  be  expedited  by  using 
cold  water.  A  small  piece  of  cloth  (an  aseptic  napkin)  is 
saturated  with  cold  water  and  held  against  the  lingual 
surface  of  the  tray.  Some  of  the  cold  water  may  be  thrown 
under  the  lip  with  a  syringe.  When  the  compound  has 
become  hard  it  is  removed  in  the  same  manner  as  a  plaster 
impression,  except  in  no  case  will  it  be  necessary  to  use  a 
spray  of  water  as  an  aid  to  loosen  it. 

Advantages  and  Disadvantages. — The  advantages  of  com- 
pound are  claimed  to  be  that  it  takes  a  sharp  impression, 
does  not  break  upon  removal,  and  compresses  the  soft 
tissues.  The  first  two  claims  are  true,  but  the  second  claim 
of  superiority  should  be  classed  as  a  disadvantage,  for  a 
material  that  does  not  break  must  bend  or  drag  when  taken 
from  an  undercut  or  dovetail-shaped  space.  The  third 
advantage  claimed  is  very  questionable.  As  ordinarily  used 
the  compression  is  not  under  the  control  of  the  operator. 
The  material  is  usually  forced  so  far  backward  upon  the 
soft  palate  as  to  produce  contraction  of  that  organ,  and  cause 


MODELLING  COMPOUND  FOR   UPPER  IMPRESSIONS    87 

depression  in  place  of  compression  at  the  palatal  border 
of  the  impression.  The  soft  tissues  upon  the  labial  and 
buccal  surfaces  are  usually  distorted.  Because  of  this  dis- 
tortion many  operators  find  it  expedient  and  useful  to 
use  a  "bead"  upon  the  maxillary  siu-face  of  labial  and 
buccal  flanges  of  an  artificial  denture.  Following  a  properly 
taken  impression,  a  bead  in  this  position  should  be  unbear- 
able. One  skilled  in  the  use  of  any  material  may  produce 
excellent  results,  but  that  is  not  evidence  that  it  is  scientific 
or  the  best.  The  confusion  existing  in  the  profession  regard- 
ing the  various  impression  materials  is  due  to  a  lack  of 
comprehension  of  the  underlying  principles. 

Where  and  How  to  Use  Modelling  Compound. — It  has  been 
stated  that  ropy  and  excessive  secretions  of  the  mouth  are 
adverse  conditions  for  retaining  artificial  dentures.  The 
method  of  oftsetting  these  untoward  conditions  will  depend 
upon  the  associated  factors.  If  they  are  accompanied  by 
a  flat  vault  and  flabby  soft  tissues  they  can  probably  be 
best  obviated  by  this  method  of  taking  the  impression.  The 
author  believes  this  is  the  one  place  in  which  a  model- 
ling compoinid  impression  is  indicated.  However,  the 
usual  method  just  described  will  in  no  wise  meet  the 
requirement.  The  principle  involved  in  this  special  impres- 
sion is  compressive  bearings  toith  a  large  vacuum  cavity  and 
vent  spaces. 

Technique. — A  suitable  size  oval  floor  tray  having  been 
selected,  the  handle  and  most  of  the  labial  and  buccal  flanges 
are  cut  away  (Fig.  35).  If  an  unsatisfactory  base-plate  has 
been  constructed  it  may  be  converted  into  an  admirable 
tray  by  cutting  away  at  least  one-half  of  the  width  of  the 
flanges.  About  one-third  of  a  cake  of  compound  is  softened, 
dried,  and  spread  over  the  warmed  maxillary  surface  of  the 
prepared  tray.  This  is  carried  into  the  mouth  and  hard 
continued  pressure  applied  so  as  to  compress  all  the  tissues 
over  the  vault  and  ridges;  at  the  same  time  the  patient  should 
comply  with  the  instruction  i)re\'iously  given  and  draw  the 
lip  and  cheeks  downward  by  hard  vigorous  muscular  action. 
This,  Dr.  J.  W.  Greene,  in  the  Greene  brothers'  method  of 


8B  IMPRESSIONS 

impression,  calls  muscle  trimming.  The  best  position  in 
which  the  operator  may  stand  while  taking  this  form  of  impres- 
sion is  directly  back  of  the  patient.  The  partially  taken 
impression  is  remoA^ed  from  the  mouth,  thoroughly  chilled, 
and  any  excess  remo^■ed.  The  peripheral  labial  and  buccal 
borders  are  warmed  over  a  small,  weak  Bunsen  flame  and 
quickly  returned  to  place  in  the  mouth.  It  is  securely  held 
in  place  with  one  hand,  and,  while  the  patient  is  muscle 
trimming,  the  operator  makes  interrupted  compression  over 
the  lip  and  cheeks  with  the  disengaged  hand.  It  may  be 
necessary  to  re-warm  and  muscle  trim  several  times,  or  an 
addition  of  soft  dry  compound  may  be  needed  upon  portions 
of  the  rim  of  the  impression.  This  addition  may  be  made  by 
"tracing  on"  with  a  stick  of  compound.  When  the  operator 
is  satisfied  that  the  rim  of  the  impression  is  perfectly  adapted 
backward  to  the  anterior  border  of  the  malar  processes,  the 
impression  is  thoroughly  chilled,  dried,  and  a  small  roll  of 
soft  modelling  compound  placed  along  the  palatal  border, 
upon  the  maxillary  surface,  and  extended  around  the  tuber- 
osities to  the  malar  processes.  This  addition  is  made  quite 
soft  in  the  small  Bunsen  flame,  carried  into  the  mouth,  and 
quickly  forced  into  place,  removed,  and  dried.  If  it  has  not 
been  sufHciently  compressed,  it  is  again  softened  and  pressed 
in  the  mouth.  The  impression  may  now  be  considered 
complete.  It  is  placed  in  cold  water  until  thoroughly  cold, 
and  without  drying  it  is  replaced  in  the  mouth  and  very  firm 
pressure  made  upon  the  lingual  surface  of  the  tray  while  the 
lip  and  cheeks  are  lifted  and  drawn  into  position  over  the 
rim  of  the  impression.  The  fingers  are  removed  from  the 
mouth  and  the  patient  requested  to  remove  the  impression. 
If  the  impression  has  been  properly  manipulated  it  may  be 
impossible  for  an  inexperienced  patient  to  remove  it.  The 
patient  should  be  instructed  to  dislodge  it  by  working  the 
lip  and  cheeks  and  closing  their  lower  teeth  upon  it  in  every 
way  possible.  Should  it  prove  to  be  insecure  at  any  place  it 
should  be  corrected,  either  by  softening  and  muscle  trimming, 
or  by  adding  soft  compound. 


MODELLING  COMPOUND  FOR  UPPER  IMPRESSIONS   89 

Rationale. — The  reason  for  this  excessively  strong  adhesion 
is  apparent.  By  this  method  of  taking  the  impression  there 
is  absokite  contact  of  the  entire  periphery  of  the  impression 
except  over  the  malar  processes,  where  there  is  an  automatic 
valve  in  the  soft  tissues  of  the  cheek.  As  the  peripheral 
border  is  forced  into  the  soft  tissues  and  either  cheek  raised, 
the  moisture  and  air  occupying  the  free  space  within  the 
impression  is  forced  out  over  the  malar  process;  then,  as  the 
cheek  is  lowered,  it  acts  as  a  valve  and  prevents  ingress  of 
air.  As  the  pressure  is  relieved  from  the  lingual  surface 
of  the  tray,  the  resilience  of  the  soft  tissues  under  the  periph- 
ery of  the  impression  causes  a  thin  vacuum  space  over 
nearly  the  whole  maxillary  surface.^ 

Fig.  36 


This  explanation  of  the  strong  retention  of  the  impression 
suggests  also  how  to  remove  the  impression,  which  is  done 
by  raising  the  cheek  and  pulling  downward  upon  the  per- 
iphery of  the  impression  at  the  malar  process.  As  air  is 
admitted  the  impression  is  loosened. 

It  should  be  apparent  that  this  method  applied  to  thin 
tense  tissues  either  would  not  produce  adhesion  or  would 
soon  become  exceedingly  painful. 

'  Thia  despription  i»  but  a  sliKlit  inodification  of  llie  Crec-ne  brothers''  method. 


90  IMPRESSIONS 

The  durability  of  such  strong  adhesion  and  its  sequence 
are  not  relevant  at  this  time,  but  will  be  discussed  in  the 
chapter  on  Retention. 

Fig.  36  is  a  modelling  compound  impression  taken  in  an 
inefficient  cast  aluminum  base-plate.  A  close  inspection 
will  show  the  muscle  trimming,  lines  showing  addition  to 
the  anterior  flange,  and  a  well-marked  line  showing  the 
compressing  portion  added  to  the  palatal  border  and  tuber- 
osities. That  the  student  may  appreciate  the  painstaking 
exactness  such  an  impress  requires,  it  is  well  to  state  that 
this  individual  impression  was  adjusted  to  the  mouth 
probably  fifteen  times,  but  the  final  result  was  good. 


IMPRESSIONS  FOR  ENLARGED  RAPHE 

Technique. — The  impression  for  this  class  is  the  same 
as  for  the  normal  class,  except  in  the  palatal  reenforcement 
wax. 

The  object  sought  with  these  enlarged  raphe  is  to  have 
contact  without  pressure.  The  palatal  reenforcement  wax 
is  adjusted  as  in  all  cases,  when  a  layer  of  the  wax  covering 
the  hard  raphe  is  removed  to  the  extent  of  yg-  of  an  inch  in 
thickness.  If  there  is  much  thickness  of  soft  tissue  upon 
each  side  of  the  hard  raphe,  a  little  additional  soft  wax  may 
be  placed  over  the  cold  reenforcement  wax  covering  the 
soft  tissue  of  the  vault,  and  readjusted  to  the  mouth  with 
moderately  firm  pressure.  Should  the  anterior  portion  of 
the  raphe  touch  the  tray,  it  must  be  relieved  by  depressing 
the  tray  (use  horn  or  wooden  mallet).  The  tray  is  filled 
with  soft  plaster  and  placed  in  the  mouth  and  pressure 
applied  back  of  the  middle  of  the  vault  of  the  tray.  This 
will  compress  the  soft  tissue  upon  each  side  of  the  hard 
raphe.  As  a  space  has  been  made  in  the  wax  covering  of 
the  hard  raphe,  some  of  the  soft  plaster  will  be  forced  back- 
ward. This  objectionable  feature  may  be  controlled  by 
having  the  patient's  head  inclined  forward. 


FULL  LOWER  IMPRESSIONS 


91 


FULL  LOWER  IMPRESSIONS 


Classification 


'  High  ridge 


I  Flat  ridges 


Broad. 

Thin. 

Broad    buccal    and    lingual 

flanges. 
Narrow    buccal    and    broad 

lingual  flanges. 
Narrow    lingual    and    broad 

buccal  flanges. 
.  Both  flanges  narrow. 


Technique. — In  all  lower  impressions  the  controlling 
factor  for  the  width  of  the  flanges  of  the  tray  will  be  the 
insertion  of  the  mylohyoid  and  the  frenum  linguie  on  the 
lingual,  and  the  buccinator  and  labial  muscles  on  the  outer 
flange.  A  rule  may  be  established  that  in  no  case  shall  the 
flange  impinge  upon  a  muscle. 

High  Ridge.^ — The  only  difference  required  for  an  impres- 
sion for  a  broad  or  thin  high  ridge  is  in  the  wax  reenforce- 
ment.  With  a  broad  ridge  the  reenforcement  is  upon  the 
lingual  flange  only,  while  for  a  thin  ridge  both  flanges  should 
be  reenforced.  Fig.  37  illustrates  a  tray  reenforced  for  a 
broad  ridge,  and  Fig.  38  is  prepared  for  a  thin  ridge. 

Broad  Ridge. — The  operator  should  assume  same  position 
in  respect  to  patient  as  mentioned  in  technique  for  uj)per 
impressions.  After  the  flanges  of  the  tray  have  been  adjusted 
for  a  broad  high  ridge,  a  roll  of  soft  wax,  about  the  size  of 
a  lead  pencil,  is  placed  upon  the  warmed  mandibular  surface 
of  the  lingual  flange,  and  inserted  in  the  mouth  in  the  same 
manner  as  described  on  page  G9,  except  that  the  floor  of  the 
tray  is  upward.  As  the  wax  is  pressed  against  the  lingual 
wall  of  the  process  the  patient  is  requested  to  raise  the  tongue 
momentarily  to  the  roof  of  the  mouth.  The  tray  is  removed, 
wax  chilled,  and  excess  cut  away.  It  is  then  filled  with 
soft  mixed  plaster  and  quickly  adjusted  in  the  mouth,  by 
first  adjusting  the  left  side,  and  then  the  right  side.    As  the 


92 


IMPRESSIONS 


Fig.  37 


Fig.  38 


FULL  LOWER  IMPRESSIONS  93 

left  side  of  the  tray  is  settled  into  position  the  finger  used  to 
distend  the  left  angle  of  the  mouth  is  carried  backward,  and 
with  the  thumb  grasps  the  cheek,  drawing  it  downward 
and  outward,  thus  preventing  a  portion  of  soft  tissue  being 
entrapped  under  the  buccal  flange  of  the  tray.  The  finger  is 
then  moved  forward  to  the  buccal  frenum,  which  is  distended, 
and  then  the  labial  frenum  is  drawn  into  place.  The  finger  is 
removed  and  the  left  thumb  inserted  across  the  mouth  as 
far  backward  as  the  angle  of  the  mouth  will  permit.  The 
fingers  will  be  under  the  mandible,  and  the  thumb  resting 
upon  both  arms  of  the  tray.  As  the  right  side  of  the  tray 
is  being  forced  into  position,  the  right  index  finger  having 
been  carried  into  the  mouth,  the  right  cheek  is  grasped  and 
drawn  out  of  the  way  of  the  buccal  flange.  Pressure  is  then 
made  over  the  border  of  the  buccal  and  labial  flanges  with 
the  fingers  of  the  right  hand.  The  thumb  of  the  left  hand 
is  then  placed  upon  the  left  side  of  the  tray  a  little  back 
of  the  angle  of  the  mouth,  while  the  right  thumb  is  placed 
in  a  like  position  upon  the  right  arm  of  the  tray.  As  the 
fingers  of  both  hands  are  pressing  firmly  against  the  under 
margin  of  the  mandible  the  tray  is  held  as  in  a  vise.  The 
patient  is  equested  to  raise  the  tongue  firmly  against  the 
roof  of  the  mouth,  after  which  it  may  rest  easily  on  the  floor 
of  the  mouth.  The  tray  should  be  he'd  firmly  until  the  plas- 
ter is  set,  when  it  is  removed  by  grasping  the  hand'e  with 
the  right  hand  and  distending  the  left  cheek  and  lip  with 
the  index  finger  of  the  left  hand. 

It  is  necessary  to  get  the  tray  and  tissues  adjusted  before 
crystallization  of  the  plaster  has  much  progressed,  therefore 
it  is  desirable  to  have  a  definite  system,  so  that  no  time  may 
be  lost.  Every  movement  should  be  positive,  but  gently 
executed. 

Thin  Ridge. — The  flanges  of  the  tray  having  been  adjusted, 
a  roll  of  soft  wax  is  placed  upon  each  flange  and  pressed  into 
position.  The  wax  cooled  and  trimmed  is  shown  in  Fig. 
38.  The  object  sought  in  this  impression  is  to  have  even 
compression  upon  the  periphery  of  the  base-plate  while 
there  is  but  slight  pressure  ui)on  the  crest  of  the  ridge.  This 
should  reliev^e  one  source  of  pain  in  artificial  dentures;  that 


94 


IMPRESSIONS 


is,  undue  pressure  upon  the  mucous  tissue  drawn  over  a 
sharp  crest  of  bone.  If  the  thin  ridge  of  gum  has  become 
pendulous,  from  excessive  resorption  of  the  process,  it  is 
well  also  to  have  it  relieved  of  pressure.  The  plaster  should 
not  be  mixed  stiff  enough  to  make  pressure  in  any  impression ; 
the  pressure  should  be  made  by  the  reenforcement  wax.  The 
plaster  is  designed  for  close  adaptation. 

Flat  Ridges. — For  these  cases  a  series  of  oval  floor  trays 
should  be  prepared  as  the  emergency  demands.  Two  or 
three  trays  of  different  sizes  prepared  for  this  class  of  cases 
will  probably  be  sufficient.    The  tray  is  prepared  by  cutting 

Fig.  39 


off  the  handle  and  about  one-half  of  the  flanges.  They 
should  be  so  trimmed  that  when  they  are  placed  in  the  mouth 
the  muscles  of  the  mandible  will  not  much  disturb  them. 

First  Subclass. — (See  classification  for  full  lower  impres- 
sions.) Either  the  regular  oval  floor  tray  with  the  flanges 
bent  outward,  or  one  of  the  specially  prepared  trays  should 
be  chosen,  as  best  fits  the  case. 

Second  Subclass. — A  regular  tray  with  the  lingual  flanges 
bent  inward  and  the  buccal  flanges  rolled  outward  and 
upward  will  probably  best  meet  the  requirements. 

Third  and  Fourth  Subclasses  will  require  the  specially 
prepared  tray. 

The  impressions  of  all  of  the  flat  ridge  cases  should  be 
taken  first  in  wax,  or,  better,  in  modelhng  compound.     If 


PARTIAL   UPPER  IMPRESSIONS  95 

the  patient  can  be  prevailed  upon  to  aid,  the  margins 
should  be  muscle  trimmed.  If  the  patient  has  not  sufficient 
control  of  the  muscles  of  the  face  so  he  can  assist,  the 
operator  must  hold  the  tray  with  the  thumb  of  one  hand 
so  that  the  other  hand  is  free  to  work  the  tissues.  The 
right  hand  should  hold  the  tray  while  working  the  tissues 
upon  the  left  side,  and  vice  versa.  The  patient  can  at  least 
l)e  pre\ailed  upon  to  forcefully  raise  the  tongue.  This 
wax  or  modelling  compound  impression  should  be  considered 
only  as  a  reenforced  tray.  Grooves  should  be  cut  in  the 
mandibular  surface  of  the  reenforcement  when  it  is  covered 
with  soft  plaster  and  inserted  in  the  mouth.  The  buccal 
tissues  must  be  removed  from  under  the  buccal  flanges  of 
the  tray  as  directed  on  page  92.  The  impression  should 
not  be  removed  from  the  mouth  until  the  plaster  is  thor- 
oughly hard.  As  the  impression  is  surrounded  by  saliva, 
there  will  be  little  danger  of  excessive  adhesion. 

Fig.  39  exhibits  full  upper  and  lower  impressions  of  the 
broad  type.  The  lower  has  the  lingual  flange  reenforced 
and  the  upper  has  the  palatal  reenforcement. 


PARTIAL  UPPER  IMPRESSIONS 

(  Anterior  teeth  lost. 
Classification'   Posterior  teeth  lost. 

(Teeth  and  spaces  alternating. 

Anterior  Teeth  Lost. — For  all  partial  cases  a  flat  floor  tray 
of  suitable  size  should  be  chosen.  If  three  or  more  teeth 
are  lost  the  vault  reenforcement  wax  of  Fig.  32  should  be 
extended  forward  to  nearly  fill  the  space  occupied  by  the 
lost  teeth.  There  should  be  about  i  of  an  inch  of  space 
between  the  wax  and  the  remaining  teeth,  also  between  the 
wax  and  gum  (Fig.  40).  Judgment  should  be  exercised  in 
the  quantity  of  plaster  used,  thus  avoiding  much  excess.  As 
[partial  plaster  impressions  are  almo.st  certain  to  be  broken 
while  removing  from  the  mouth,  a  small  tray  (lacquer  or 
metal;  and  tweezers  should  be  upon  the  bracket  table,  so  that 
the  pieces  may  be  placed  in  order  as  they  are  removed  from 


96 


IMPRESSIONS 

Fig.  40 


Fig  41 


PARTIAL   UPPER  IMPRESSIONS  97 

the  mouth.  Figs.  49  and  5o  ilhistrate  such  an  arrangement. 
Fig.  41  is  a  tray  properly  filled  with  plaster  for  taking  an 
impression  where  the  four  upper  incisors  are  missing.  The 
plaster  should  be  mixed  just  stiff  enough  so  it  will  not  run 
when  placed  in  the  tray.  This  implies  that,  because  of  its 
stiffness,  the  time  of  setting  is  shortened,  and  that  it  must 
be  quickly  adjusted.     In  such  a  partial  case  the  lingual 

Fig.  42 


aspect,  and  possibly  the  occlusal  surface  of  the  teeth,  is 
desired.  The  buccal  surface  is  not  only  not  needed  in  the 
impression,  but  comi)licatcs  the  removal  materially. 

With  the  loss  of  any  increasing  number  of  teeth  backward, 
the  reenforcement  wax  is  extended ;  the  technique  is  the  same 
as  just  described.    Fig.  42  illustrates  the  wax  reenforcement 
for  the  lost  ten  anterior  teeth, 
7 


98  IMPRESSIONS 

Posterior  Teeth  Lost. — This  class  implies  that  the  remaining 
anterior  teeth  are  in  phalanx  and  that  there  are  distally  no 
isolated  teeth.  In  such  cases  a  flat  floor  tray  should  have  the 
reenforcement  wax  as  in  Fig.  43.  This  prepared  tray  is  for  a 
case  with  the  teeth  lost  distal  to  the  first  bicuspids.  Fig.  44 
has  the  plaster  suitably  placed. 

Fig.  43 


Teeth  and  Spaces  Alternating. — Fig.  45  is  a  tray  suitably 
reenforced.  In  all  partial  cases,  except  where  wax  contact 
is  desired,  there  should  be  a  space  for  plaster  over  the  wax 
reenforcement  of  i  of  an  inch  or  little  more.  The  alternating 
spaces  may  be  dovetail-shape.  In  such  cases  cores  should 
be  made  of  wax  to  fill  them.  Fig.  46  is  a  plaster  cast  showing  a 
space  between  the  second  bicuspid  and  second  molar  requiring 
a  core.  In  the  illustration  the  core  is  attached  to  the  upper 
surface  of  the  cast.  The  core  is  made  by  filling  the  space 
(without  drying  the  teeth)  full  of  soft  wax.  Most  of  the 
excess  wax  may  be  trimmed  away  in  the  mouth.     The  wax  is 


PARTIAL   UPPER  IMPRESSIONS  99 

Fig.  44 


Fig.  45 


100 


IMPRESSIONS 


made  cold  and  removed  through  the  wider  aspect  of  the 
space.  In  this  instance  it  should  be  pushed  inward.  The 
wax  is  then  thoroughly  chilled  and  trimmed  pyramid-shape, 


Fig.  46 

wBm^            ~ 

i| 

■ 

^^^^K''. 

J 

k 

d 

1 

Fig.  47 


with  the  base  resting  upon  the  gum.  Fig.  47  shows  the  core 
in  place.  After  it  has  been  cooled  and  trimmed  (pyramid- 
shape),  so  the  plaster  will  draw  from  it,  it  is  secured  in  place 


PARTIAL   UPPER  IMPRESSIONS 


101 


by  slightly  pinching  the  occlusal  end.  If  there  are  large 
spaces,  as  for  the  incisor  teeth,  the  tray  should  be  reenforced 
as  shown  in  Fig,  40.  After  the  impression  has  been 
removed  from  the  mouth,  the  wax  is  carefully  removed  and 
replaced  in  the  impression. 

Isolated  Teeth  Method. — Fig.  48  shows  a  cast  with  the  two 
cuspids  and  the  left  second  bicuspid  remaining.  The  teeth 
were  short  and  firmly  attached,  so  there  was  no  danger  of 
their  extraction  in  the  impression.  In  this  case  all  the  prepa- 
ration necessary  was  the  reenforcement  of  the  tray  as  in  Fig. 
43.     However,  if  the  teeth  had  been  long  and  bell-shaped. 


Fia.  48 


and  loose,  it  would  then  have  been  necessary  to  have  thor- 
oughly dried  the  teeth  (one  at  a  time),  and  to  have  molded 
a  little  soft  wax  about  the  neck  of  each  tooth  as  it  was 
dried.  The  plaster  impression  would  either  draw  away  from 
the  wax,  when  it  should  have  been  replaced  in  the  impres- 
sion, or  the  wax  would  have  remained  in  the  impression. 
Had  the  teeth  dragged  through  the  wax  no  harm  would 
have  been  done  other  than  a  slight  distortion  of  the  wax. 
Fig.  49  is  the  impression  taken  for  the  cast  shown  in  Fig.  48. 


102 


IMPRESSIONS 


Some  of  the  reenforcement  wax  is  shown;  also  the  fragments 
are  placed  in  order  about  the  main  portion  of  the  impres- 
sion.   Fig.  50  shows  the  assembled  pieces  luted  together  with 


wax. 


FiG^  49 


MS 

i>-M?vi  JH|caV-- / 

f  -^          ■/. 

*fi 

Detachable  Tray  Method. — In  this  method  no  wax  reen- 
forcement should  be  used,  except  as  in  Fig.  45;  and  this 
should  be  so  trimmed  that  there  are  no  undercuts.  The 
maxillary  surface  of  the  tray  and  reenforcement  wax  are 
smeared  with  a  thin  layer  of  vaseline.  This  will  permit  the 
tray  to  part  from  the  hardened  plaster,  which  may  be 
removed  in  sections  after  the  manner  used  by  orthodontists. 
The  maxillary  surface  of  the  tray  should  be  smooth,  and 
in  no  degree  dovetail-shape.  If  this  method  is  to  be  used, 
the  operator  should  first  carefully  observe  the  teeth  and 


PARTIAL   UPPER  IMPRESSIONS 


103 


vacancies,  and  devise  a  scheme  for  notching  and  breaking  the 
plaster  in  sections.  The  notching  and  breaking  is  done  with 
a  stout  knife  which  must  be  well  guarded  so  the  patient 
may  not  be  injured.  As  the  pieces  are  removed  from  the 
mouth  they  are  placed  in  order  on  the  lacquer  tray.  The 
impression    tray   may   be   removed    from   the   mouth   and 

Fig    50 


^^^^^^^^■^^P^a^H 

■| 

^^ 

^^^^f^  ■^^. '.  ^B 

P^ 

^^V  ^          '^^ 

|. 

^f   ^ 

\ 

^V^^^^i^^L,  ^^_ 

J 

notches  cut  in  the  plaster,  but  no  attempt  should  be  made 
to  break  the  plaster  away  from  the  teeth  until  it  will  make 
a  clean  break,  that  is,  not  crush.  The  inexperienced  student 
should  be  very  cautious  oF  choosing  this  method,  because 
of  the  danger  from  the  knife.  However,  the  tray  may  part 
from  an  impression  unexpectedly,  when  it  becomes  necessary 
to  notch  and  remove  the  impression  in  sections. 


104 


IMPRESSIONS 


PARTIAL  LOWER  IMPRESSIONS 

Classification. — The  classification  used  for  partial  upper 
impressions  is  applicable  for  lower  ones.  The  wax  reenforce- 
ments  are  the  same  except  that  there  is  no  vault  and  in  place 
of  a  palatal  margin  reenforcement,  a  lingual  flange  reenforce- 
ment  is  required.  Rarely  should  any  lower  impression 
(either  partial  or  full)  be  taken  without  the  lingual  flange 
being  reenforced.     This  is  necessary  to  control  the  folds  of 


Fig.  51 


the  soft  tissues,  and  the  submaxillary  and  sublingual  glands 
that  are  occasionally  very  troublesome.  In  all  cases  the 
mylohyoid  muscle  influences  the  loosely  attached  mucous 
membrane  for  a  long  distance  above  the  origin  of  the  muscle, 
and  draws  it  inward  and  upward.  As  a  result,  if  the  lingual 
flange  compression  wax  is  not  used  the  lingual  flange  of  the 
completed  artificial  denture  will  not  lie  close  to  the  mandible. 
This  is  often  a  source  of  annoyance  to  the  patient. 


PARTIAL  LOWER  IMPRESSIONS  105 


Fio.  52 


Fig.  53 


106 


IMPRESSIONS 


Fig,  51  shows  a  flat  floor  lower  tray  with  reenforcement. 
Fig.  52,  with  the  plaster  in  place  ready  for  insertion.  Fig. 
53  shows  the  impression  with  the  fragments  and  a  core. 
Fig.  54  is  the  assembled  impression.  Fig.  55  is  a  Weiss  tray 
(a  modification  of  the  type  shown  in  Fig.  22)  and  fragments. 
This  tray  requires  the  lingual  flange  reenforcement  only. 
Fig.  56  is  the  assembled  impression. 


Fig.  54 


Impression  Aphorisms — 1.  An  impression  constitutes  the 
foundation  upon  which  the  success  of  an  artificial  denture 
depends. 

2.  A  suitable  impression  can  be  obtained  only  by  studying 
the  case  and  devising  a  definite  scheme  of  procedure. 

3.  A  stock  tray  should  be  adapted  to  the  individual  case, 
by  bending,  trimming,  and  the  addition  of  reenforcement. 

4.  Compression  should  be  made  through  a  properly 
formed  tray.  No  impression  material  has  discriminating 
power,  hence  cannot  be  depended  upon  to  make  suitable 
compression. 


IMPRESSION  APHORISMS 


107 


5  Plaster  of  Paris  is  the  best  impression  material  because 
of  its  plasticity,  adaptability,  rigidity,  friability,  and  con- 
trollability. 


Fig.  55 


6  Modelling  compoun.l  is  valuable  in  specific  cases 
because  of  its  rigidity  and  workableness.  It  is  very  delusive 
because  of  its  toughness.         .      ,      ,  ,  .,  •    •   .^ii; 

7.  An  impression  material  is  of  value  only  as  it  is  inteiii- 

gentlv  and  skilfully  worked. 

8  Plaster  of  Paris  is  aseptic  because  it  can  be  used  but 
once.     Modelling  compound  is  dangerous  because  it  ma> 


108 


IMPRESSIONS 


be  used  repeatedly  and  cannot  be  sterilized  by  heat  without 
destroying  its  working  properties. 


Fig.  56 


9.  Small  simple  impressions  may  be  taken  either  in  plaster 
of  Paris,  modelling  compound,  or  wax.  The  accuracy  will 
be  in  the  order  named. 

10.  The  more  difficult  the  case  the  more  essential  is  the 
plaster-of-Paris  impression. 


CHAPTER     III 

CASTS 

Definition. — A  cast  is  a  reproduction  in  plaster  of  Paris, 
its  compounds,  or  some  plastic  material,  of  an  object  or  part, 
made  from  an  impression  or  mold.  Casts  are  used  to  give 
their  negative  likeness  to  an  artificial  denture. 

Unfortunately  there  is  much  confusion  in  dental  nomen- 
clature in  the  use  of  the  term  cast  and  model.  There  is  no 
authority  outside  of  the  dental  profession  for  calling  a  cast 
a  model,  as  is  too  commonly  done  in  vulcanite  nomenclature; 
and  such  indifference  in  the  use  of  technical  terms  can  only 
lower  one  in  the  estimation  of  learned  people.  "Cast"  is 
from  kasto,  throw,  and  is  used  in  the  sense  of  throwing, 
pouring,  or  forming  a  plastic  material  in  a  mold  or  impression. 
The  term  "cast"  is  applied  to  objects  made  of  plaster  of 
Paris,  wax,  and  similar  substances,  while  the  term  casting  is 
usually  applied  to  metallic  objects  formed  in  molds. 

Model  is  from  modus,  measure,  and  is  defined  as  an  object 
representing  accurately  something  to  be  made  or  already 
existing;  a  material  pattern  of  natural,  heroic,  or  diminutive 
size.  Model  is  differentiated  from  pattern  in  that  a  pattern 
is  usually  flat,  while  a  model  has  material  contour. 

In  sculpture,  the  model  is  the  plaster  or  clay  original  of 
the  work  to  be  executed  in  stone  or  metal;  a  person  who 
does  duty  as  a  copy  for  painters  or  sculptors. 

A  sculptor  may  idealize  his  living  model;  but  his  workman 
must  exactly  copy  the  clay  model  made  for  him. 

Even  the  dressmaking  trade  uses  the  term  model  correctly. 
They  use  a  model  to  give  its  form  to  the  human  body,  also 
to  the  external  surface  of  the  garment.  It  is  only  an  incident 
that  the  garment  is  made  over  the  model,  for  the  object 
sought  is  to  gi\e  form  to  the  outer  surface  of  the  garment. 


no  CASTS 

The  photographer  speaks  of  his  negative,  not  of  his  pattern 
or  model.  If  he  uses  the  term  model,  he  uses  it  correctly 
and  applies  it  to  his  subject,  not  to  the  intermediate,  the 
negative. 

A  dentist  uses  casts,  castings,  and  models,  and  he  should, 
if  he  is  a  member  of  a  learned  profession,  differentiate  and 
use  his  terms  intelligently  and  correctly.  A  cast  is  anything 
formed,  while  in  a  plastic  state,  in  a  mold  or  impression; 
casting  (noun)  is  a  term  applied  to  metal  casts;  and  model  is 
an  object  to  be  copied,  but  it  is  a  positive,  not  a  negative 
copy.  Of  all  the  arts,  sciences,  and  crafts,  dentistry  alone 
uses  the  term  in  both  a  positive  and  negative  sense.  Such 
use  is  entirely  inexcusable,  because  it  leads  to  confusion  of 
thought;  besides,  there  is  no  dearth  of  correct  terms  in 
common  use. 

It  is  interesting  to  note  the  origin  of  this  use  of  the  term 
viodel  in  dentistry.  At  the  time  of  the  introduction  of  vul- 
canite, during  the  fifties  of  the  last  century,  plaster  models 
were  in  constant  use  for  constructing  dies  for  metal  base- 
plates. As  vulcanite  work  is  constructed  upon  the  plaster 
form  in  place  of  a  metal  form,  it  was  only  natural  that  the 
familiar  term  model  should  be  retained  for  the  new  use. 
Unfortunately,  the  teachers  and  writers  of  text-books  at  the 
time  of  the  introduction  of  vulcanite  did  not  give  sufficient 
thought  to  the  philology  of  the  glossary  required  for  the  new 
art;  hence,  some  of  the  terms  that  have  come  down,  even  to 
this  day,  are  not  scientific. 

A  plaster  model  is  never  used  in  vulcanite  work  as  ordin- 
arily constructed.  Plaster  casts  are  used.  A  plaster  cast 
gives  its  negative  likeness  only  to  the  inner  surface  of  a 
vulcanite  denture,  therefore  cannot  correctly  be  called  a 
model.  Orthodontists  make  plaster  casts  of  cases  as  records 
of  progress  and  completion.  A  plaster  cast  becomes  a  model 
only  when  it  is  used  for  duplication.  The  patient's  jaws  are 
the  models,  not  their  plaster  reproduction. 

Uses  for  Casts. — There  are  two  general  uses  for  casts  in 
dentistry:  (1)  As  a  form  over  which  something  is  constructed; 
(2)  as  a  model  or  copy. 


SPENCE  PLASTER  COMPOUND  111 

Materials  for  Casts. — The  material  for  casts  must  be 
chosen  with  regard  to  the  process  to  be  employed.  The 
materials  may  be  classified  as:  (1)  Plaster  of  Paris;  (2)  Spence 
plaster  compound;  (3)  plaster  compounds  known  as  "invest- 
ment compounds;"  4)  wax  and  its  compounds  as  models  for 
metal  castings. 

Plaster  for  Casts. — From  the  study  of  the  expansion,  con- 
traction, and  compressibility  of  plaster,  it  is  obvious  that  its 
use  is  limited,  and  that  dental  operations  often  require 
casts  that  are  less  subject  to  change  by  heat  and  pressure. 
While  some  operators  are  accustomed  to  use  building  plasters 
for  certain  purposes,  it  is  better  to  select  from  the  various 
compounds  of  plaster  for  dental  use  the  one  designed  for  the 
work  at  hand.  Failures  and  imperfections  due  to  the  use  of 
unsuitable  material  may  thus  be  avoided.  For  all  purposes, 
when  little  heat  or  pressure  is  to  be  used,  French's  regular 
dental  plaster  serves  an  excellent  purpose.  This  plaster  is 
found  in  all  well-stocked  dental  supply  houses,  and  is  the 
only  plaster  carried  by  many  of  them. 

Spence  Plaster  Compound. — ^This  is  an  excellent  prepara- 
tion of  plaster  of  Paris,  Portland  cement,  and  chemicals  to 
control  its  setting  and  expansion  properties.  This  material 
has  four  times  the  strength  of  dental  plaster,  and  the  expan- 
sion is  nearly  at  zero.  As  the  material  is  now  placed  upon 
the  market,  if  properly  worked,  its  setting  time  is  about 
the  same  as  slow  setting  dental  plaster.  Dr.  Stewart  J. 
Spence,  of  Chattanooga,  Tenn.  has  certainly  produced  a 
very  valuable  material  for  casts  which  are  to  be  subjected 
to  moderate  heat  and  considerable  pressure.  It  is  especially 
adapted  for  casts  for  vulcanite  work. 

It  may  be  well  at  this  time  to  consider  tersely  the  important 
addition  to  plaster  in  the  production  of  this  compound. 

Portland  Cement. — This  term  was  first  used  in  1824,  and  was 
given  to  a  patented  cement  manufactured  at  Leeds,  England. 
It  is  made  by  calcining  and  grinding  a  suitable  mixture  of 
lime  and  clay.  It  may  be  considered  as  a  silicate  of  lime 
and  alumina.  There  is  a  greater  variety  of  cements  grouj)ed 
under  the  general  heading  of  Portland  cement  than  of  plaster. 


112  CASTS 

The  student  should  not  consider  that  any  mixture  of  cement 
purchased  upon  the  market  and  plaster  will  answer  the  same 
purpose  as  that  bearing  the  name  of  Spence,  because  the 
Spence  compound  is  the  result  of  much  study  and  experimen- 
tation. 

IVorking  SiJence  Plaster  Compound. — The  mixing  of  this 
compound  with  water  is  much  more  laborious  than  mixing 
plaster  of  Paris.  The  ratio  of  water  to  the  compound,  as 
now  placed  upon  the  market,  is  one  to  four.  For  a  cast  a 
fluidounce  of  water  is  placed  in  the  plaster  bow  and  three 
measured  ounces  of  the  compound  are  added  and  thoroughly 
spatulated  with  a  very  stiff  spatula  until  it  becomes  soft  and 
plastic,  after  which  a  half-ounce  more  may  be  thoroughly 
incorporated.  The  remaining  half -ounce  may  be  better 
added  one-half  at  a  time.  It  must  be  spatulated  and  kneaded 
in  a  bowl  until  the  mass  is  putty-like  in  consistency,  and  if 
on  continued  w^orking  it  becomes  too  soft,  more  of  the  com- 
pound should  be  added.  When  properly  mixed  it  can  be 
handled  with  the  fingers  and  requires  to  be  well-packed  and 
jarred  in  filling  the  impression. 

Investment  Compound  Casts. — This  class  of  casts  is  designed 
to  stand  high  heat,  and  must  be  made  of  a  material  suitable 
for  its  intended  use.  The  supply  houses  furnish  many  of 
these  compounds,  w^hich  answer  a  good  purpose.  They  consist 
largely  of  plaster  of  Paris  for  a  bond  to  combine  the  material 
and  such  materials  as  will  well  withstand  high  heat,  either 
singly  or  in  combination.  Of  the  materials  used  may  be 
named:  Sand  (silica),  clay,  lime,  asbestos,  pulverized  cal- 
cined fireclay,  Portland  cement,  oxide  of  iron,  pumice 
stone,  chalk,  etc. 

Working  Investment  Compound  Materials. — These  materials 
are  worked  at  about  the  consistency  of  plaster  of  Paris. 
Owing  to  the  small  quantity  of  plaster  they  contain,  they  will 
require  much  less  water  than  pure  plaster;  usually  one 
measure  of  water  to  three  or  four  of  investment  compound. 

Price's  Artificial  Stone. — This  is  a  recent  material  invented 
by  Dr.  Weston  A.  Price,  of  Cleveland.  It  is  a  silicate  cement, 
and    when   properly  manipulated    it   becomes   very   hard, 


CASTS  FOR  ARTIFICIAL  DENTURES  113 

strong,  unchangeable,  and  will  withstand  the  highest  heat 
of  any  compound  known  in  the  dental  laboratory. 

How  Worked. — The  powder  is  mixed  with  the  liquid  accom- 
panying it,  upon  a  mixing  slab,  with  a  spatula.  It  is  then 
formed  into  the  mold  or  impression  of  wax,  or  over  the  wax 
model.  It  is  permitted  to  set  for  a  few  hours,  after  which  it 
is  heated  to  a  full  red  heat;  it  is  then  hard  and  unchangeable. 
It  is  excellent  for  that  for  which  it  is  designed,  but  is  not 
suitable  for  ordinary  investments. 

Wax  and  Compounds. — There  are  a  variety  of  preparations 
in  the  dental  supply  houses  composed  of  wax,  paraffin,  gum, 
and  terpine.  They  are  formed  in  a  mold  or  impression, 
and  then  the  wax  cast  is  used  as  a  model  for  producing  a 
metal  casting.  This  material  is  often  carved  into  form  for  a 
model.  Such  a  model  cannot  be  spoken  of  as  a  cast  because 
it  was  not  formed  in  a  cavity. 


CASTS  FOR  ARTIFICIAL  DENTURES 

The  construction  of  plaster  casts  only  will  be  further  con- 
sidered in  this  chapter,  but  in  discussing  each  variety  of 
artificial  denture  the  cast  suitable  for  the  work  will  be 
described. 

Use  of  Impressions. — The  preceding  chapter  treated  of 
impressions  and  how  to  obtain  them.  This  chapter  treats 
of  the  use  of  the  impression.  All  base-plate  artificial  dentures 
are  constructed  over  either  a  cast  or  casting,  therefore  for 
each  artificial  denture  it  is  necessary  to  obtain  a  suitable 
impression  from  which  a  cast  is  obtained.  This  implies 
that  there  is  a  technique  for  preparing  the  impression  and 
making  the  cast. 

Preparing  the  Impression. — A  plaster  impression  is  often 
broken  in  removing  it  from  the  mouth.  Indeed,  often  a  plaster 
impression  can  be  removed  only  by  fracturing.  The  property 
of  being  easily  broken  is  one  of  the  valuable  features  of 
plaster  of  Paris.  This  insures  its  removal  and  the  accuracy 
of  imprint  when  the  fragments  are  assembled.  The  impres- 
8 


114  CASTS 

sion  having  been  removed  (if  broken,  the  fragments  arranged 
in  order  upon  a  small  tray),  it  is  permitted  to  dry  for  a  few 
minutes  (five  to  thirt^O?  when,  any  small  particles  of  plaster 
having  been  removed  with  an  ox-hair  brush,  or  a  pointed 
instrument  if  necessary,  the  fragments  are  accurately 
readjusted  in  the  impression  tray  and  secured  with  melted 
wax  (Figs.  50  and  54).  If  any  carving  is  to  be  done  upon 
the  impression,  it  should  be  done  at  this  stage  of  the  pro- 
cedure. However,  as  any  carving  must  be  done  for  a  specific 
purpose,  instruction  as  to  where  and  how  to  do  it  can  be 
given  only  in  describing  the  work  requiring  such  treatment. 
The  impression  is  next  treated  with  a  separating  fluid  to 
facilitate  the  removal  of  the  impression  from  the  cast. 

Separating  Fluids.^ — The  object  of  the  separating  fluid  is 
to  so  treat  the  surface  of  the  impression  that  a  perfect  coun- 
terpart of  the  intaglio  may  be  formed  .of  plaster  or  its  com- 
pounds, and  the  two  easily  separated.  This  is  accomplished 
by  flowing  over  the  surface  of  the  impression  some  material 
that  will  prevent  adhesion  of  the  added  plaster.  The 
desirable  properties  for  a  separating  medium  are  as  follows: 
(1)  It  should  add  as  little  substance  as  possible  to  the  surface 
of  the  impression;  (2)  it  should  provide  a  line  of  demarcation 
with  a  distinct  penetration  of  the  impression;  (3)  it  should 
not  cause  chemical  changes  and  injurious  effects  upon  either 
the  surface  of  the  cast  or  the  denture  to  be  constructed  over 
it;  and  (4)  it  should  give  a  smooth  glazed  surface  to  the  cast. 
There  are  a  great  variety  of  materials  recommended  and  used 
for  this  purpose,  but  few  are  extensively  used.  They  may  be 
classified  as:  Alcoholic  solutions:  (a)  shellac,  (b)  sandarac, 
and  (c)  other  gums  and  terpenes  added  to  these  foundation 
solutions.  Aqueous  solutions:  (a)  liquid  silex  (silicate  of  soda), 
(6)  soap,  (c)  borax  and  shellac,  (d)  ammonia  or  other  alkaline 
substances  and  shellac.  Oils,  as  sperm,  lard,  sweet,  or 
vaseline;  and  ethereal  solutions:  (a)  of  soap  and  (6)  collodion. 
The  aniline  dyes  are  used  as  coloring  matter  for  some  of  these 
preparations.  Many  of  these  preparations  are  kept  in  stock 
by  the  supply  houses,  and  some  of  them  under  fanciful  names. 

Perhaps  the  best  and  most  commonly  used  method  is  to 


CASTS  FOR  ARTIFICIAL   DENTURES 


115 


first  saturate  the  surface  of  the  impression  with  a  thin 
alcohoHc  solution  of  shellac,  and  when  dry,  to  apply  one  or 
more  coats  of  alcoholic  solution  of  sandarac.  These  varnishes 
are  made  by  dissolving  one  ounce  of  either  gum  in  4  ounces  of 
alcohol.  The  solution  is  greatly  facilitated  by  heating  the 
uncorked  bottle,  containing  the  gum  and  alcohol  in  simmering 
water  for  a  half-hour  or  until  dissolved.  The  stock  bottle 
should  be  kept  well  corked.  If  either  varnish  becomes  too 
thick   (by    evaporation),  it    should    be    thinned    with    cold 


Fig.  57 


alcohol.  The  varnishes  are  applied  to  the  impression  with 
a  camel's-hair  brush.  Each  coat  should  be  permitted  to  dry 
before  applying  another.  The  shellac  varnish  will  penetrate 
and  give  a  yellowish  color  to  the  plaster  of  the  impression 
for  ttV  of  an  inch,  which  is  a  warning  of  the  approach  to  the 
cast  when  cutting  away  the  plaster  impression.  This  may  be 
seen  in  Fig.  57.  If  the  pla.ster  is  not  well  colored,  it  should 
be  given  another  coat  of  shellac,  after  which  it  is  given  one 
or  more  coats  of  sandarac  varnish.  The  shellac  penetrates 
and  gives  depth  of  color  line,  and  the  sandarac  remains  upon 
the  surface  and  forms  a  glaze. 


116  CASTS 

Pouring  the  Impression. — This  is  a  common  term  used  for 
filling  the  impression.  The  term  is  slightly  misleading  in 
that  it  implies  that  the  plaster  mix  is  poured  into  the  impres- 
sion. The  plaster  batter  should  be  a  little  thicker  than  for 
an  impression  and  a  trifle  too  thick  to  pour.  However,  it 
must  not  be  so  stiff  that  it  will  not  flow  perfectly  over  the 
surface  of  the  impression  when  jarred  by  rapping  the  tray 
lightly  upon  the  table.  The  same  rule  (as  to  the  ratio  of 
water  and  plaster)  is  used  for  casts  as  for  impressions — that 
is,  one  measure  of  water  and  two  measures  of  regular  dental 
plaster.  If  the  mix  seems  too  thin,  more  dry  plaster  should 
be  added  until  the  mix  will  stand  as  placed.  However, 
it  must  have  a  pronounced  glossy  or  watery  appearance,  and 
when  this  characteristic  diminishes  it  is  evidence  that  either 
too  much  plaster  has  been  added  or  that  crystallization  has 
commenced.  The  surface  of  the  impression  should  be  thor- 
oughly covered  before  this  deadened  appearance  begins. 
The  student  should  observe  carefully  the  appearance  of  his 
plaster  mixes,  because  the  quality  of  the  cast  depends  much 
upon  the  manipulation.  An  excessive  amount  of  plaster 
added  to  the  water  or  overspatulation  interferes  with  the 
process  of  crystallization,  thus  causing  increased  expansion 
and  reduced  strength  of  the  cast. 

Technique  for  Filling  the  Impression.- — The  surface  of  the 
impression  having  been  properly  varnished  while  dry,  it 
should  then  be  immersed  in  water  until  bubbles  cease  to 
form,  the  plaster  gauged,  and  smoothly  and  quickly  mixed ;  a 
portion  of  the  mix  (about  a  teaspoonful)  is  placed  upon  the 
higher  central  portion  of  the  impression  and  caused  to  flow 
into  the  lower  portions  of  the  intaglio  by  rapping  the  tray 
three  or  four  times  upon  the  plaster  bench.  Portion  after 
portion  of  the  mix  is  added  and  jarred  into  position  until  the 
intaglio  of  the  impression  is  full,  when  the  jarring  ceases  and 
the  remainder  of  the  mix  is  piled  on  and  spread  with  the 
spatula  until  the  plaster  forming  the  cast  is  about  one-half 
inch  thick  over  the  highest  portion  of  the  vault. 

Shape  for  a  Plaster  Cast.^ — For  the  sake  of  convenience  it  is 
well  to  adopt  such  a  form  as  will  be  best  adapted  to  the 


CASTS  FOR  ARTIFICIAL  DENTURES 


117 


various  uses  to  which  a  cast  may  be  put.  A  suitable  form 
not  only  favors  and  expedites  future  operations,  but  in  some 
cases  it  affords  additional  strength.  The  form  affording  the 
greatest  usefulness  is  the  truncated  cone.  This  form  is 
easily  given  to  the  cast  by  inverting  the  tray  while  the 
plaster  is  somewhat  soft  and  gently  pressing  it  down  upon 


Fig.  58 


any  smooth  surface,  as  a  slab  of  marble,  glass,  or  metal.  If 
the  base  of  the  cast  is  formed  upon  any  rigid  material,  the 
surface  should  be  slightly  oiled,  to  facilitate  the  removal 
of  the  plaster.  (A  convenient  arrangement  is  to  have  a 
0-inch  square  block  of  wood  covered  with  sheet  zinc.  This 
will  need  no  oiling,  for  the  sheet  metal  is  flexible  and  will 
yield  to  pressure  applied  at  the  sides  of  the  cast.)     After 


118  CASTS 

the  filled  tray  is  inverted  upon  the  smooth  surface  the  plaster 
spatula  should  be  passed  about  it,  producing  a  smooth  and 
symmetrical  outline.  The  truncated  cone  form  of  an  upper 
cast  will  not  be  a  symmetrical  truncated  cone,  for  its  base 
will  be  a  parabola;  and  the  lower  one  will  be  horseshoe- 
shape.  Instructors  are  accustomed  to  direct  that  the  base 
of  a  lower  cast  should  be  made  solid  (for  strength)  in  place 
of  a  horseshoe-shape.  It  is  better  to  sacrifice  a  portion  of 
the  strength  of  the  lower  cast  for  the  convenience  obtained 
in  antagonization  of  the  teeth.  Fig.  58  illustrates  properly 
formed  upper  and  lower  casts. 

Separating  Cast  from  Impression. — There  are  three  steps  to 
this  operation — (a)  removing  any  plaster  overhanging  the 
edge  of  the  tray,  (6)  removing  the  tray  from  the  impression, 
and  (c)  removing  the  impression  from  the  cast. 

A  sharp  plaster  knife  is  used  to  cut  away  any  overhanging 
plaster  so  that  the  outer  edge  of  the  tray  is  visible. 

If  the  impression  is  either  wax  or  plaster,  the  outer  surface 
of  the  tray  should  be  slightly  warmed  over  a  Bunsen  flame. 
The  heat  applied  to  the  tray  will  soften  the  wax  in  contact 
with  the  tray,  and  the  two  may  be  easily  parted.  The  plaster 
impression  is  as  easily  removed  from  the  tray  as  a  wax  one, 
provided  heat  sufficient  to  soften  wax  is  passed  through  the 
tray  (Fig.  59).  This  is  probably  accomphshed  by  slightly 
expanding  the  metal  of  the  tray,  and  also  by  generating  a 
small  amount  of  steam  between  the  tray  and  plaster,  or  at 
least  the  expansion  of  the  moisture  upon  the  surface  of  the 
impression  next  to  the  tray.  A  modelling  compound  impres- 
sion can  be  readily  removed  by  rapping  upon  the  outer  sur- 
face of  the  tray.  If  the  tray  is  of  such  shape  that  the  two 
are  dovetailed  together,  the  rapping  method  may  not  suffice, 
and  heat  should  be  applied.  This  can  be  best  done  by 
placing  it  in  a  dish  of  cold  water  and  applying  slow  heat. 
Care  must  be  exercised  not  to  apply  too  much  heat  or  the 
modelHng  compound  will  be  made  very  adhesive  and  will 
adhere  both  to  the  tray  and  cast. 

Separating  the  impression  from  the  cast  can  be  neatly 
done  by  the  exercise  of  care.    Wax  should  be  slowly  warmed 


CASTS  FOR  ARTIFICIAL  DENTURES 


119 


over  a  soft  flame,  and  modelling  compound  in  water  Either 
material  should  be  removed  from  the  cast  by  lifting  the  outer 
portions  and  turning  them  over  upon  the  central  mass  when 
it  is  easilv  removed.  While  a  separating  fluid  is  not  neces- 
sarilv  applied  to  wax  and  modelling  compound  impressions, 
nevertheless,  if  a  thin  coat  of  sandarac  is  dried  upon  either 
impression  before  filling,  it  does  facilitate  tlie  ^^^oval  of  the 
impression  material,  pro^•ided  it  has  been  slightly  overheated. 


Fig.  59 


Plaster  impressions  may  be  groupee  into  two  classes  to 
conform  to  as  many  procedures  for  separating  them  from 
their  casts:  (1)  Flat  impressions  without  undercuts  It  is 
not  necessar>-  to  remove  these  impressions  from  the  tray 
but  by  holding  them  with  the  cast  downward  and  gently 
rapping  upon  the  tray  they  will  drop  from  the  impression, 
sfpfominent  flaring  processes.  .  The  plaster  inipression 
should  be  carefully  pared  away,  with  a  ^^^^  P^^  ^J^^^^"  ^^^ 
over  the  crest  of  the  alveolar  process,  until  the  shellac  line 
o  demarcation  is  visible.  The  outer  flange  ot  the  impression 
may  then  be  flaked  away..  The  remaining  cenrapoioii 
provided  it  is  not  keyed  into  place,  may  be  1  tted  out  by 
fnserting  the  point  of  the  knife  or  a  wax  spatula  under  any 


120  CASTS 

convenient  edge  of  the  impression.  Should  the  central 
portion  not  yield  to  reasonable  force,  it  must  be  carefully 
notched  along  the  median  line,  when  first  one  half  and 
then  the  other  may  be  pushed  inward. 

Casts  of  Partial  Cases. — The  principle  of  construction  of 
partial  cases  is  the  same  as  for  full  cases,  but  the  technique 
varies  to  suit  the  conditions.  Care  must  be  exercised,  in 
applying  the  separating  fluid  to  the  imprint  of  the  teeth,  that 
every  portion  may  be  thoroughly  covered.  This  may  be 
facilitated  by  applying  an  excessive  amount  of  fluid,  and 
using  a  rotary  movement  of  the  brush,  or  it  may  be  applied 
with  a  pledget  of  cotton  held  in  a  pair  of  tweezers.  While 
drying,  the  impression  should  be  inverted  so  that  any  excess 
may  not  settle  into  the  depressions  of  the  impression.  If 
the  impression  has  been  standing  for  a  half-hour  it  should 
be  dipped  in  water  and  the  excess  water  shaken  out  just 
before  filling.  If  the  impression  has  been  standing  for 
several  hours,  it  should  stand  in  water  for  three  or  four  minutes 
before  filling.  This  will  aid  the  flow  of  the  plaster  and  help 
to  prevent  air  bubbles  forming  in  the  plaster  of  the  cast. 
The  filling  plaster  should  be  caused  to  flow  down  one  side 
of  the  deep  depressions  (as  the  intaglio  of  the  teeth),  thus 
permitting  the  air  to  escape  from  the  other.  It  is  well  also 
to  have  a  tamping  stick  to  press  into  the  imprints  of  the 
teeth.  (A  small  riveting  hammer  handle  with  the  head  cut  off 
at  the  smallest  part  of  the  neck  is  an  excellent  tamper.  Use 
either  end  as  convenience  requires).  Each  added  portion 
of  plaster  should  be  jarred  into  place.  Much  care  is  required 
in  removing  the  impression  from  the  cast.  It  must  first  be 
carved  down  to  the  shellac  line  of  demarcation  before  any 
attempt  is  made  at  breaking  away  the  impression.  An 
excellent  way,  used  by  many  for  strengthening  isolated 
plaster  teeth  of  a  cast  is,  as  soon  as  the  intaglio  of  the  tooth 
is  filled  with  soft  plaster,  to  force  into  the  centre  of  each 
tooth,  for  its  entire  length,  a  pin  or  a  small  diameter  f-inch 
wire  brad.  Fig.  57  shows  a  plaster  cast ^  with  the  plaster 
about  the  isolated  teeth  carved  ready  for  breaking  away  the 
impression.    Fig.  48  shows  the  cast. 


CASTS  FOR  ARTIFICIAL  DENTURES 


121 


Repairing  Broken  Casts. — Plaster  casts  may  be  broken 
accidentally.  These  may  be  nicely  and  strongly  mended  by 
uniting  the  sections  with  moderately  thin,  well  spatulated 


Fig.  60 


Fig.  61 


oxyphosphate  of  zinc  cement.  The  sections  should  be 
supported  until  the  cement  has  set  sufficiently  to  be  unyield- 
ing to  the  weight  of  them.  The  cast  should  then  be  undis- 
turbed for  at  least  a  half-hour.     If  the  cement  is  properly 


122 


CASTS 


mixed  and  the  portions  of  the  cast  are  well  pressed  together, 
the  resulting  union  should  be  very  strong. 

Base-plate  Outline. — With  a  soft  lead  pencil  the  outline 
of  the  periphery  of  the  denture  is  traced  upon  the  cast. 
Figs.  60  and  61  show  the  base-plate  outlines  for  an  upper 
and  lower  denture. 

Fig.  62 


Fig.  62  illustrates  knives  for  cutting  plaster.  ^  is  a  common 
form ;  B  is  a  Wilson  knife  having  a  2|-inch  draw  blade  and  a 
l|-inch  push  blade;  C  is  a  saddler's  knife.  The  saddler's 
knife  is  a  powerful  tool  for  trimming  the  base  of  casts  only. 
It  is  used  with  a  rocking  motion.  All  plaster  knives  need 
frequent  grinding,  as  plaster,  and  especially  Spence  com- 
pound, quickly  blunts  the  edge. 


CHAPTER    IV 

OCCLUSION  AND  CONTOUR  MODELS 

Use. — Occlude,  to  strike  against  or  close.  This  term  is 
used  to  represent  the  teeth  closed  in  their  natural  position 
of  ease  and  rest.  In  this  state  the  condyles  of  the  mandible 
are  in  their  most  retruded  position  in  their  glenoid  fossee, 
except  in  a  few  cases  of  acquired  abnormal  condyle  articu- 
lation. It  is  apparent  that  to  construct  an  artificial  denture 
much  data,  other  than  a  cast  of  the  jaw  upon  which  a  base- 
plate is  to  be  worn,  is  necessary,  in  securing  which  the  occlu- 
sion model  is  an  important  factor.  This  occlusion  model  is 
a  mass  of  material  roughly  outlined,  and  indicating  the 
normal  (probably  the  natural)  relation  of  the  teeth  and  jaws 
while  at  rest.  The  term  "contour"  is  added  to  the  title  to 
imply  that  the  mass  of  material  has  been  molded  or  carved 
to  such  a  form  as  will  give  the  desired  contour  to  the  external 
soft  tissues  of  the  lower  third  of  the  face.  Therefore,  if  this 
mass  of  material  which  we  call  the  occlusion  and  contour 
model  is  truly  a  model  pattern  it  must  be  accurately  repro- 
duced in  the  essentials  which  it  represents.  However,  this 
does  not  mean  that  the  forms  of  the  teeth  should  be  carved 
in  these  models  because  the  teeth  are  not  to  be  made  by  the 
prosthetist  (they  may  be  obtained  of  the  trade  in  much 
better  form  and  strength  than  would  be  possible  to  produce 
in  the  dental  laboratory);  but  it  does  mean  that  the  lines 
indicated  by  the  occlusion  and  contour  models  are  to  be 
permanently  retained.  This  implies  that  thought  and 
technique  are  to  be  employed  in  constructing  these  models. 
The  student  should  have  fixed  in  his  mind  the  idea  that  the 
two  primary  objects  of  these  models  are  to  establish  the 
position  of  the  artificial  teeth  when  at  rest,  and  to  give 


124  OCCLUSION  AND  CONTOUR  MODELS 

harmonious  contour  to  the  soft  tissues  covering  the  artificial 
dentures.  In  addition  to  these  primary  factors  they  are 
used  to  record  other  important  data,  such  as  the  high  and 
low  lip  lines,  also  the  median  line  and  the  slit  of  the  lips. 
They  may  record  the  plane  of  the  teeth,  and  aid  in  estab- 
lishing the  condyle  path ;  or  they  may  ignore  the  plane  of  the 
teeth  and  establish  the  condyle  path. 

Materials  Used. — Wax  and  its  combinations,  modelling 
compound,  gutta-percha,  resinous  preparations,  and  possibly 
plaster  of  Paris,  may  be  named  as  the  materials  of  which 
occlusion  and  contour  models  are  made.  These  materials 
are  used  by  the  profession  in  the  order  named.  The  materials 
are  attached  to  a  base-plate,  either  a  temporary  one  or 
the  base-plate  upon  which  the  teeth  are  to  be  permanently 
mounted. 

Wax  is  most  commonly  used  as  well  as  most  misused  for 
the  purpose  under  consideration. 


THE  BITE 

This  term  is  generally  used  in  connection  with  the  use  of 
wax  for  obtaining  the  relation  between  the  jaws  and  teeth. 
The  word  bite  is  of  Anglo-Saxon  origin,  and  means  "split;" 
hence  it  is  used  in  the  sense  of  cut,  lacerate,  take  severe  hold 
of,  and  similar  ideas.  As  applied  to  dental  technology,  it 
means  to  cut  into  a  mass  of  soft  wax  with  the  teeth  or  bare 
gums.  The  term  is  inelegant  and  unscientific,  and  except 
for  a  very  limited  use  it  is  non-expressive  and  associated  with 
pernicious  methods.  The  term  should  never  be  applied  to 
occlusion  and  contour  models.  The  term  wax-bite  is  known 
by  several  other  inelegant  terms,  as  mush-bite,  quash-bite, 
hunk-bite,  and  like  terms.  They  all  refer  to  the  common 
practice  of  placing  a  mass  of  wax  in  the  mouth  and  requiring 
the  patient  to  bite  into  it.  To  bite,  cut:  As  in  95  per  cent, 
of  cases  the  upper  incisors  overlap  the  lower  incisors,  to  bite 
or  cut  means  to  bring  the  lower  incisors  forward  and  in 
contact  with  the  upper  incisors,  thus  inviting  the  patient 


THE  BITE  125 

to  do  the  thing  that  is  the  hete  noire  of  the  dentist  in  mounting 
artificial  teeth.  The  first  requirement  in  obtaining  the 
desired  relation  between  the  jaws  and  teeth  is  that  the 
mandible  shall  be  in  its  most  retruded  position.  There  is 
but  one  class  of  cases  where  the  prosthetist  should  ever  use 
the  quash-bite,  and  that  is  where  there  are  two  or  more 
natural  teeth  that  have  the  required  occlusion,  but  not 
enough  points  of  contact  to  support  the  casts  while  being 
attached  to  the  articulated  frames.  If  contour  and  other 
data  provided  by  occlusion  and  contour  models  are  not 
desired,  then,  and  then  only,  may  the  quash-bite  be  used 
advantageously.  As  an  illustration  of  an  appropriate  place 
to  use  a  quash-bite,  an  imaginary  case  may  be  considered, 
consisting  of  a  full  lower  natural  denture  and  the  six  anterior, 
right  first  bicuspid  and  left  second  molar  remaining  in  the 
upper  jaw,  the  bicuspid  and  molar  only  in  occlusion.  Such 
a  case  would  be  the  most  favorable  imaginable  for  casts 
with  only  two  points  of  contact  being  self-sustained;  and  it 
is  surprising  to  the  student,  no  matter  how  he  may  have 
bolstered  the  casts  with  pieces  of  wax  before  mounting  on 
the  articulated  frames,  to  find  how  much  the  finished  den- 
tures may  be  off  from  perfect  occlusion.  This  is  easily 
understood  when  consideration  is  given  to  the  points  of 
contact  as  fulcra  and  the  distant  positions  for  the  left  first 
bicuspid  and  right  second  molar  as  ends  of  a  lever.  A  very 
slight  movement  at  the  fulcra  will  mean  relatively  a  large 
amount  at  the  ends  of  the  lever.  A  modification  of  this 
supposed  case  would  be  having  the  retained  second  molar 
upon  the  right  side,  it  would  then  be  evident  that  some 
means  of  establishing  the  relationship  of  the  left  side  would 
be  necessary.  As  a  result  of  the  consideration  of  these 
imaginary  cases  this  rule  may  be  established:  All  partial 
cases,  unless  they  have  three  or  more  widely  separated 
points  of  occlusal  contact,  require  occlusion  guides.  Quash- 
bites  may  serve  an  excellent  purpose  as  occlusion  guides.  A 
suitable  quash-bite  for  the  case  just  considered  would  be  to 
form  a  crescent-shaped  mass  of  soft  wax  of  a  little  greater 
thickness  than  the  space  between  the  teeth  of  the  lower 


126  OCCLUSION  AND  CONTOUR  MODELS 

jaw  and  the  gum  of  the  upper  jaw,  and  having  embedded  in 
it  a  14-gauge  soft  iron  wire  stiffener.  This  prepared  mass  of 
wax  is  placed  just  inside  the  anterior  teeth,  with  the  ends 
occupying  the  edentulous  spaces.  The  patient  is  then  in- 
structed to  close  and  hold  the  teeth  together  firmly.  The 
operator  should  press  against  the  extruding  wax,  molding 
it  firmly  against  the  buccal  surfaces  of  the  teeth  and  gums. 
The  patient  is  then  instructed  to  open  the  mouth  moderately 
wide,  when  the  operator  should  remove  the  wax  with  as 
little  distortion  as  possible.  It  should  then  be  made  hard 
by  placing  in  cold  water,  after  which  it  is  dried,  trimmed 
of  excess  wax,  and  a  small  roll  of  soft  wax  placed  in  the 
imprint  of  the  gums.  It  is  then  readjusted  in  the  mouth 
and  the  mouth  firmly  closed  upon  it.  This  will  correct  any 
imperfections  caused  by  manipulating  the  soft  mass  of  wax. 
In  using  this  wax  occlusion  guide  care  should  be  exercised 
to  see  that  excessive  portions  of  plaster  or  wax  do  not  prevent 
the  plaster  casts  going  fully  to  place.  Usually  the  casts  or 
wax  guides  will  require  considerable  trimming  to  permit  of 
adjustment. 

Occlusion  models  require  a  well-adjusted  base-plate.  The 
base-plate  of  the  artificial  denture  being  permanently  con- 
structed is  the  very  best  that  can  be  provided  for  occlusion 
models.  In  fact,  the  best  results  can  only  be  obtained  in 
artificial  dentures  by  first  constructing  the  base-plate.  This 
statement  will  invite  disagreement,  nevertheless  the  state- 
ment is  tenable  and  will  be  demonstrated.  However,  where 
the  single  vulcanization  method  is  to  be  employed  in  making 
an  artificial  denture,  a  temporary  base-plate  will  necessarily 
be  constructed  for  the  occlusion  model.  There  are  several 
materials  used  for  this  purpose,  as  y  6"~iiich  thick  sheets  of 
wax,  paraffin,  modelling  compound,  gutta-percha  and 
"ideal  base-plate,"  and  similar  preparations  obtainable  at 
the  supply  houses.  These  preparations  are  composed  of 
shellac  or  a  similar  substance. 

Methods  for  forming  a  base-plate  of  tin  are  used  by  a  few 
operators,  as  swaging  a  base-plate  of  sheet  block-tin,  and 
by  burnishing  tinfoil  over  the  cast.      Excellent  results  by 


THE  BITE  127 

the  burnishing:  method  may  be  obtained  by  the  following 
technique:  Adapt  a  sheet  of  No.  20  tinfoil  to  the  plaster 
cast  with  the  fingers  and  thumbs;  the  surplus  is  cut  away  with 
scissors,  after  which  the  tin  is  burnished  with  a  steel  or  agate 
burnisher.  Care  should  be  exercised  not  to  use  sufficient 
force  to  mar  the  face  of  the  cast.  A  second  sheet  is  adapted 
to  the  burnished  sheet  by  the  fingers  and  thumbs,  removed, 
and  trimmed.  A  small  dab  of  thick  sandarac  varnish  is 
placed  upon  the  centre  of  the  burnished  sheet  when  the 
second  sheet  is  readjusted  and  burnished,  beginning  at  the 
centre  and  working  outward.  Layer  after  layer  is  thus 
added  until  the  required  thickness  is  obtained.  After  the 
first  sheet  of  No.  20  is  adjusted  a  heavier  foil  may  be  used  if 
preferred. 

Paraffin  Base-plate. — Paraffin  is  found  in  the  supply  houses 
in  the  form  of  thin  sheets  put  up  in  half-pound  boxes.  It  is 
usually  called  pink  wax  because  of  the  color  the  manufacturers 
have  given  it.  This  material  is  used  by  slightly  warming 
it  over  a  smokeless  flame  and  adapting  it  to  the  plaster 
cast.  The  excess  base-plate  wax  is  trimmed  away  with  a 
warm  wax  spatula  at  the  indicated  peripheral  outline  of  the 
artificial  denture.  An  excellent  addition  may  be  made  to 
this  paraffin  base-plate  by  first  adapting  a  sheet  of  tinfoil 
to  the  cast.  This  will  prevent  the  paraffin,  if  overheated, 
from  adhering  to  the  cast,  and  also  add  some  rigidity  to  the 
base-plate.  The  principal  objection  to  wax  or  paraffin  as  a 
base-plate  is  that  it  is  not  rigid  enough  to  retain  its  form 
while  adjusting  the  occlusal  model,  and  later  the  mounted 
teeth,  to  the  mouth.  For  this  reason  some  operators  make 
this  temporary  base-plate  of  modelling  compound,  gutta- 
percha, or  of  the  various  resinous  preparations  offered  for 
sale.  The  temporary  base-plate  having  been  formed  over  the 
cast,  it  is  well  to  try  it  in  the  mouth  and  prove  the  correct- 
ness of  its  adaptation  and  peripheral  outline.  This  is  not 
very  satisfactorily  done  with  the  less  rigid  base-plate,  but 
with  the  permanent  base-plates  of  vulcanite  or  metal  it  is 
a  most  important  step  in  the  procedure.  Mention  is  made 
of  this  fact  to  impress  the  idea  that  the  most  commonly 


128  OCCLUSION  AND  CONTOUR  MODELS 

used  method  is  the  most  unsatisfactory  and  unreliable  one. 
The  base-plate  (when  adjusted)  is  removed  from  the  mouth, 
dried,  and  replaced  upon  the  cast,  a  roll  of  softened  pure 
yellow  wax  is  molded  over  the  ridge  of  the  base-plate  to  the 
estimated  length  and  fulness  of  the  lip,  when  it  is  tried  in 
the  mouth  and  manipulated  to  the  required  contour.  (The 
full  details  of  contouring  the  occlusion  model  can  only  be 
properly  considered  under  the  subject  of  Esthetics,  Chapter 
XVI.)  The  edge  of  the  wax  rim  should  come  to,  and  thus 
indicate,  the  slit  of  the  lips.  If  the  occlusion  model  is  an 
upper  one  to  be  adapted  to  a  full  lower  artificial  or  natural 
denture,  the  occlusal  border  of  the  wax  rim  must  be  trimmed 
to  evenly  press  upon  the  opposing  denture.  It  is  not  neces- 
sary to  trim  so  as  to  have  perfect  contact  of  the  occlusal 
border,  but  there  must  be  at  least  four  well-spaced  points  of 
contact,  then  a  small  flattened  roll  of  soft  wax  placed  along 
the  occlusal  border  and  closed  upon  will  make  perfect  con- 
tact. If  the  occlusion  models  are  being  formed  for  an  upper 
and  lower  edentulous  case,  the  occlusal  border  should 
represent  the  plane  of  the  teeth  (see  Chapter  I).  This  is 
accomplished  by  having  the  occlusal  border  of  the  upper 
model  exactly  at  the  slit  of  the  lips  and  extending  straight 
backward  parallel  with  the  imaginary  line  drawn  from  the 
base  of  the  nose  to  the  lower  border  of  the  external  auditory 
meatus,  or  the  line  dividing  the  middle  and  lower  thirds 
of  the  face  (Fig.  1). 

Modelling  Compound  Technique. — The  following  descrip- 
tion is  a  quotation  from  Dr.  Charles  R.  Turner,  in  the 
American  Text-book  of  Prosthetic   Dentistry: 

"For  the  Upper  Jaw. — To  construct  a  bite-plate  of  modelling 
composition  for  the  upper  jaw,  the  cast  should  be  placed 
upon  its  base  on  the  work-bench  with  the  distal  portion 
toward  the  operator.  The  method  of  making  the  bite-plate 
in  one  piece  proposed  by  Dr.  W.  W.  Evans  is  to  be  recom- 
mended. Three-fourths  of  a  cake  of  modelling  composition 
is  softened  in  warm  water,  kneaded  in  the  hands  until  homo- 
geneous, and  rolled  into  an  ellipsoid  about  two  inches  long. 
One  side  of  this  should  be  thinned  out  by  pressure  between 


THE  BITE  129 

the  fingers,  and  the  mass  so  placed  upon  the  cast  that  the 
thinned  portion  projects  sHghtly  beyond  the  posterior  margin 
of  the  plate  outline.  By  manipulation  with  the  thumbs  the 
remainder  of  the  compound  is  gradually  worked  forward  so 
that  the  vault  of  the  cast  is  covered  by  it  to  the  thickness 
of  about  ^V  of  an  inch.  The  thickness  of  this  may  be  readily 
gauged,  for  the  cast  chills  the  material  as  it  comes  in  contact 
with  it,  thus  hardening  it,  while  the  overlying  soft  portion 
may  be  pushed  forward.  When  the  top  of  the  alveolar  ridge 
has  been  reached,  the  compound  should  be  carried  over  it 
and  slightly  beyond  the  plate  outline,  along  the  labial  and 
buccal  surfaces,  the  most  of  the  mass,  however,  remaining 
upon  the  ridge  and  being  shaped  to  represent  the  occlusal 
portion  of  the  bite-plate.  The  probable  relation  of  this  part 
of  the  artificial  denture  to  the  alveolar  ridge  and  the  prob- 
able fulness  of  the  buccal  and  labial  portions  should  be  borne 
in  mind  and  the  compound  disposed  accordingly,  since  the 
bite-plate  when  completed  should  be  a  rough  model  for  the 
denture  in  these  particulars.  It  should  be  taken  from  the 
cast,  chilled  in  cold  water,  and  trimmed  around  its  periphery 
to  the  plate  outline.  It  ought  then  to  be  replaced  upon  the 
cast  and  its  margin  brought  into  close  contact  therewith, 
around  the  plate  outline.  This  is  to  insure  firm  retention 
of  the  plate  in  the  mouth,  which  is  of  the  greatest  importance, 
and  should  be  secured,  even  if  it  be  necessary  to  make  at  this 
time  the  changes  in  the  surface  of  the  cast  which  provide  for 
the  adhesion  of  the  future  denture.  The  form  of  the  bite- 
plate  at  this  time  is  largely  tentative,  as  it  is  purposed  to 
complete  its  modelling  when  the  bite  is  taken,  in  accordance 
with  the  requirements  which  shall  then  be  indicated.  During 
the  process  of  forming  the  plate,  to  prevent  adhesion,  the 
hands  should  be  wet  and  the  compound  occasionally  taken 
off  the  cast  to  break  up  its  adhesion  while  it  is  soft,  and  then 
replaced,  but  under  no  circumstances  must  the  cast  be  wet, 
as  this  will  injure  it  for  subsequent  use.  Rubbing  its  surface 
with  soapstone  or  talcum  powder  will  effectually  prevent 
the  adhesion  of  the  compound. 

"It  is  possible  to  construct  the  plate  in  two  portions,  that  in 
9 


130  OCCLUSION  AND  CONTOUR  MODELS 

contact  with  the  mucous  membrane  being  made  of  one  piece 
of  modelhng  compound  rolled  into  a  thin  sheet  and  adapted 
to  the  cast,  that  representing  the  occlusal  portion  being 
formed  of  a  roll  bent  to  the  shape  of  the  alveolar  ridge,  and 
made  to  adhere  by  dry  heat.  The  occlusal  portion  is  made 
of  wax  by  some  practitioners  because  of  the  greater  ease  with 
which  it  may  be  carved,  but  its  softness  and  tendency  to 
yield  under  pressure  make  it  less  safe  than  modelling  com- 
pound in  preserving  a  fixed  distance  between  the  jaws. 

"The  Lower  Bite-plate. — The  lower  bite-plate  is  more  easily 
made  than  the  upper.  With  the  cast  face  up  on  the  work- 
bench, a  piece  of  compound  equal  to  about  one-half  of  a 
sheet  is  softened  and  worked  into  a  long  uniform  roll,  bent 
to  the  shape  of  the  alveolar  process,  and  placed  upon  its 
summit.  With  the  thumbs  and  fingers  it  is  worked  down 
the  lingual  and  labial  sides  to  a  poiut  slightly  beyond  the 
plate  outline,  that  portion  over  the  ridge  being  shaped  to 
represent  this  part  of  the  future  lower  plate  and  made  to 
correspond  in  outline  to  the  arch  of  the  upper  bite-plate.  It 
is  removed  and  trimmed  to  the  plate  outline  like  the  upper, 
its  occlusal  surface  being  left  rough.  If  the  lower  plate  must 
be  very  thin,  it  may  be  strengthened  by  embedding  in  it  a 
piece  of  iron  or  brass  wire  shaped  to  conform  to  the  alveolar 
outline." 

Modelling  Compound  Base-plate. — The  preceding  method, 
as  described  by  Dr.  Turner,  consists  of  forming  the  base- 
plate and  occlusion  model  of  one  piece.  Another  method  is 
to  form  the  base-plate  of  a  thin  sheet  of  modelling  compound 
and  building  up  the  occlusion  and  contour  portion  with 
yellow  or  pink  wax. 

Technique. — The  plaster  cast  is  covered  with  a  sheet  of  tin- 
foil or  pattern  tin,  by  adjusting  the  tin  with  the  thumb  and 
finger.  It  is  not  necessary  to  adjust  the  foil  accurately,  for 
the  following  step  of  adapting  the  modelling  compound  will 
perfectly  adjust  the  foil.  The  modelling  compound  should 
be  rolled  or  pressed  into  a  sheet  yV  to  ^-j  of  an  inch  thick. 
The  sheet  may  be  formed  by  rolling  with  a  moistened 
wooden  roller  or  pressing  it  with  the  fingers  upon  a  warm 


THE  BITE  131 

plate  of  glass.  The  glass  slab  should  be  slightly  lubricated 
with  vaseline,  or  moistened  with  water,  to  prevent  adhesion. 
The  warm  and  pliable  sheet  of  modelling  compound  is  quickly 
and  accurately  adjusted  to  the  plaster  cast  over  the  tinfoil, 
and  trimmed  to  the  peripheral  outline  of  the  desired  plate. 
The  tinfoil  serves  a  double  purpose;  it  renders  easy  the 
removal  of  the  base-plate  from  the  cast,  and  prevents  soiling 
of  the  cast  should  the  compound  be  overheated  in  any  sub- 
sequent operation.  Any  portion  of  the  modelling  compound 
base-plate  that  may  not  be  perfectly  adjusted  may  be  per- 
fected by  passing  repeatedly  over  the  Bunsen  flame  and 
conforming  with  the  fingers  slightly  moistened. 

Gutta-percha  and  the  Resinoid  Preparations. — These  are 
obtained  at  the  supply  houses  in  sheets  about  ^\  of  an  inch 
thick.  They  are  both  manipulated  in  the  same  manner  as 
the  thin  sheets  of  modelling  compound,  and  will  not  need 
further  description. 

Vulcanite  Base-plate. — This  form  of  base-plate  is  applica- 
ble only  where  there  is  considerable  recession  of  the  alveoli. 
It  is  apparent  that  a  vulcanite  base-plate  must  have  con- 
siderable thickness  for  strength  and  rigidity;  and  admit  of 
sufficient  added  material  to  attach  the  teeth  and  to  give  the 
indicated  restoration  without  overdistending  the  supported 
soft  tissues. 

The  advantages  of  a  vulcanite  base-plate  are:  (1)  It  detects 
a  faulty  impression  before  much  work  has  been  done.  (2)  It 
permits  study  of  the  retention  of  the  artificial  denture.  If 
it  is  evident  that  the  impression  was  defective,  or  that  the 
devised  scheme  for  retention  is  insufficient,  a  new  impression 
may  be  taken  and  the  mistakes  corrected  without  much  loss 
of  time  and  labor.  {?))  It  gives  stability  and  proper  support 
to  the  subsequent  operation  of  construction. 

The  only  disadvantage  in  the  vulcanite  base-i)late,  where 
it  is  indicated,  is  that  the  finished  artificial  denture  has  a 
portion  of  its  substance  overvulcanized,  consequently  it  is 
harder  and  more  brittle  than  it  W(juld  have  been  if  vulcan- 
ized bnt  once.  This  slight  weakening  of  a  portion  of  the 
vulcanite  will  do  no  harm  provided  the  appliance  is  correctly 


132  OCCLUSION  AND  CONTOUR  MODELS 

constructed.  However,  the  student  should  know  that  it  is 
essential  that  the  heavy  bearings  of  the  base-plate  upon  the 
tissues  must  be  properly  located,  and  that  there  is  danger  of 
warping  in  the  second  vulcanization.  This  phase  of  the 
subject  will  be  considered  in  the  technique  of  double  vulcan- 
ization. 

Vulcanite  Base-jjlate  Technique. — A  suitably  prepared  cast 
of  plaster  of  Paris  or  Spence  plaster  compound  having  been 
obtained,  it  is  preferably  (though  not  necessarily)  overlaid 
with  a  sheet  of  thin  tinfoil,  after  which  a  sheet  of  slightly 
softened  paraflfin  (pink  wax)  is  accurately  adjusted  to  the 
cast  over  the  tin  protection.  The  excess  wax  and  tin  are 
cut  away  at  the  previously  indicated  peripheral  outline  for 
the  base-plate.  The  edge  of  the  wax  base-plate  is  then  care- 
fully sealed  to  the  cast  with  a  hot  wax  spatula.  An  additional 
layer  of  wax  ma}^  be  added  over  any  portion  of  the  base- 
plate, at  the  discretion  of  the  operator.  Such  an  addition  is 
especially  indicated  over  the  crest  of  the  lower  base-plate 
as  a  means  of  obtaining  sufficient  stiffness. 


Fig.  63 


The  cast  and  model  base-plate  is  flashed  in  a  Star  or  Wilson 
flask,  the  flask  opened,  model  base-plate  removed,  surface 
of  the  cast  finished,  (either  silex  or  tin),  packed  with  rubber, 
flask  closed,  and  the  case  vulcanized.  After  the  vulcanization 
is  complete  and  the  vulcanizer  cold,  the  base-plate  is  removed 
from  the  flask,  cleaned  of  plaster,  the  edges  filed,  and  the 
outer  surface  scraped  to  give  a  suitable  surface  for  the 
attachment  of  the  rubber  at  the  time  of  second  vulcanization. 
The  inner  surface,  or  the  surface  to  rest  upon  the  soft  tissues 
should  not  be  changed  except  to  remove  any  excrescences 


OCCLUSION  AND  CONTOUR  MODELS  133 

produced  by  defects  on  the  surface  of  the  cast.  Fig.  63 
shows  a  vulcanite  base-plate. 

This  outline  sketch  has  introduced  several  laboratory 
processes,  which  will  be  discussed  in  their  proper  place. 

Metal  Base-plates. — When  an  artificial  denture  is  to  be 
constructed  upon  a  metal  base,  the  base-plate  is  formed 
either  by  the  casting  or  swaging  method.  It  is  obvious  that 
the  base-plate  constructed  as  a  component  part  of  the 
finished  artificial  denture  is  the  very  best  base-plate  for  the 
occlusion  and  contour  models.  Therefore,  the  vulcanite  and 
metal  base-plates  are  to  be  much  preferred  to  the  temporary 
base-plates  formed  of  wax  or  of  the  gum  or  resinous  prepara- 
tions. 

OCCLUSION  AND  CONTOUR  MODELS 

The  base-plate,  of  whatever  material,  having  been  adjusted 
to  the  mouth,  the  walls  of  the  model  are  to  be  built  up  of 
either  pure  yellow  beeswax,  white  w^ax,  pink  wax  (paraffin),  or 
modelling  compound.  Their  rigidity  is  in  the  inverse  order 
as  named.  The  ease  of  manipulation  is  in  the  order  given. 
The  }'ellow  wax  is  the  least  rigid,  but  because  of  its  ease  of 
manipulation  it  is  most  commonly  used  for  building  up  the 
occlusion  walls.  The  student  should  constantly  bear  in 
mind  this  one  deficiency  of  yellow  wax,  although  the  material 
is  commended  to  him  because  of  its  desirable  i)roi)erties  for 
subsequent  procedures.  No  matter,  at  this  time,  which 
material  is  selected,  the  material  will  be  manipulated  in  the 
same  manner,  so  far  as  construction  is  concerned.  Having 
placed  the  base-plate  on  the  cast,  a  cylindrical  roll  of  the 
softened  material  of  sufficient  length  to  cover  the  crest  of  the 
alveolar  ridge,  and  in  diameter  varying  from  i  to  i  of  an 
inch,  according  to  the  amount  of  space  to  be  filled,  is  con- 
formed by  manipulating  with  the  fingers  and  thumbs  to  the 
ridge  portion  of  the  base-plate.  The  plastic  material  is  luted 
to  the  base-plate  by  the  use  of  a  hot  spatula.  The  labial  and 
buccal  surfaces  are  added  to  or  carved  away  as  may  be 
necessary  to  give  the  required  contour  for  the  support  of  the 


134 


OCCLUSION  AND  CONTOUR  MODELS 


lip  and  cheeks.  This  first  shaping  is  entirely  by  guesswork; 
however,  this  is  only  to  give  it  general  form  for  trying  in 
the  mouth.  The  esthetic  manipulation  of  the  plastic  material 
to  the  mouth  will  be  treated  of  in  the  chapter  on  Esthetics. 
The  occlusal  surface  of  the  plastic  rim  must  be  a  perfectly 
flat  surface,  and  as  this  edge  forms  the  occlusal  plane  or  teeth 
plane,  it  must  be  correctly  located.  The  perpendicular 
length  of  the  plastic  rim  is  indicated  by  the  length  of  the 
lip,  and  is  located  by  the  slit  of  the  mouth  when  the  lips  are 
perfectly  relaxed  and  at  rest.    The  slit  of  the  lip  maiks  the 


Fig.  64 


anterior  border  of  the  plastic  rim,  but  from  that  point  back- 
ward the  length  is  indicated  onl^  by  the  naso-auditory- 
meatus  line  (see  Fig.  1,  also  Chapter  I).  The  occlusal 
surface  is  carved  from  or  added  to  until  the  required  plane 
is  obtained.  The  method  of  testing  this  wax  plane  is  to 
place  the  occlusion  model  in  the  mouth,  and  a  straight  edge 
placed  against  the  occlusal  surface  and  extending  4  inches 
from  the  mouth  will  indicate  whether  the  occlusal  surface 
of  the  occlusion  model  is  parallel  with  the  naso-auditory- 
meatus  line  or  not  (Fig.  64).     Should  the  student  have 


OCCLUSION  AND  CONTOUR  MODELS  135 

trouble  in  carrying  this  naso-auditory-meatus  line  with  his 
eye,  he  can  stretch  a  string  so  as  to  include  the  two  points 
named,  thus  ascertaining  whether  the  string  and  straight 
edge  are  parallel  or  not.  A  suitable  straight  edge  may  be 
formed  of  a  thin  sheet  of  metal,  horn,  or  vulcanite.  It  should 
be  2  inches  wide  at  one  end  and  6  inches  long.  After  the 
correct  occlusal  plane  has  been  established  and  any  defi- 
ciencies noticed  filled  in,  the  occlusion  model  is  pressed  upon  a 
flat  surface  with  sufficient  force  to  give  a  true  even  plane  to 
the  occlusal  surface  of  the  model.  At  all  times,  in  using  any 
force  upon  a  base-plate,  it  should  be  upon  the  plaster  cast, 
thus  avoiding  any  possibility  of  warping.  Prevention  is 
always  better  than  remedying. 

The  upper  occlusion  model  having  been  perfected,  it  is 
removed  from  the  mouth  and  placed  in  cold  water. 

The  lower  model  is  built  up  in  the  same  manner  as  the 
upper  and  then  adjusted  to  the  upper  in  the  mouth.  The 
upper  model  is  kept  in  cold  water  except  during  the  few 
moments  at  a  time  that  it  is  needed  in  the  mouth  while 
adjusting  the  lower.  By  keeping  the  upper  model  cold  and 
rigid,  all  change  resulting  from  closing  the  mouth  will  be  in 
the  softer,  lower  model.  The  lower  model  must  be  manipu- 
lated until  it  has  a  suitable  vertical  length,  contour,  and  an 
even  pressure  upon  the  occlusal  surface  of  the  upper  model. 
The  occlusion  models  having  been  satisfactorily  adjusted, 
they  are  removed  and  placed  in  cold  water  to  thoroughly 
chill. 

The  patient  should  be  instructed  regarding  the  next  step 
of  the  operation,  that  is,  retruding  and  protruding  the  chin. 
Often  it  will  require  considerable  time  and  patience  to 
educate  the  patient  in  placing  the  chin  as  requested.  It  is 
not  necessary ;  in  fact,  it  is  better  that  the  patient  should  not 
place  the  chin  in  the  extreme  protruded  position.  They 
should  place  it  in  the  extreme  retruded  position  and  pro- 
trude it  at  least  one-fourth  of  an  inch.  A  hand  mirror  is 
often  an  aid  to  the  patient  in  learning  to  protrude  and 
retrude  the  chin.  If  the  patient  does  not  readily  do  as 
requested,   the  operator  may   demonstrate   with   his   own 


136  OCCLUSION  AND  CONTOUR  MODELS 

mouth  the  desired  movements.  The  patient  having  become 
proficient  in  the  exercise,  the  occlusion  models  are  adjusted 
in  the  mouth.  Should  either  of  the  models  be  refractory  and 
not  keep  its  place,  it  may  be  temporarily  "glued"  into  place 
by  sprinkling  the  inner  surface  with  powdered  gum  trag- 
acanth.  The  patient  is  requested  to  retrude  the  mandible 
and  close  the  jaws,  then  to  protrude  and  close.  These 
instructions  being  satisfactorily  obeyed,  the  patient  is 
requested  to  retrude  the  mandible,  close  the  jaws,  and  hold 
the  occlusion  models  firmly  together.  The  head  is  then 
moderately  tilted  backward.  The  patient  is  requested  to 
swallow.  The  act  of  deglutition  necessarily  places  the  man- 
dible in  the  retruded  position.    While  the  occlusion  models 

Fig.  65 


are  thus  firmly  occluded,  the  lips  are  parted  and  the  median 
line  of  the  face  is  marked  upon  both  models  with  a  sharp 
instrument.  The  patient  is  requested  to  raise  the  upper  lip  as 
high  as  possible  by  muscular  action.  Then  a  horizontal  line 
is  made  indicating  the  highest  point  at  which  the  lip  can  be 
raised.  The  lower  lip  is  depressed  and  the  low  lip  line 
traced.  The  cheeks  are  distended  and  two  perpendicular  or 
oblique  lines  are  drawn  upon  each  buccal  surface.  These 
buccal  lines  must  extend  into  both  the  upper  and  lower 
models  and  are  used  as  location  marks  only  (Fig.  65).. 
There  are  now  registered  upon  the  occlusion  models  the  slit 
of  the  lips,  the  median  line  of  the  face,  and  the  high  and  low 
lip  lines.     Besides  these  lines  used  in  mounting  the  teeth, 


OCCLUSION  AND  CONTOUR  MODELS  137 

there  are  four  buccal  lines  used  in  conjunction  with  the 
median  line  to  properly  assemble  the  models  when  out  of 

the  mouth.  ,  i    ,  e 

Condyle  Path —The  next  record  to  be  made  by  means  ot 
the  occluding  models  is  the  condyle  path.  By  reference  to 
Figs  2  and  5,  and  Chapter  I,  it  will  be  seen  that  there  is  a 
great  variation  of  the  condyle  path,  that  the  prnicipal  portion 
of  the  path  is  a  straight  and  more  or  less  oblique  line,  but 
if  the  mandible  is  protruded  to  its  extreme  position  the  con- 
dyle has  described  a  "straightened  out"  letter  S  rather  than 
a^nearlv  straight  line;  therefore,  in  taking  this  measurement 
the  extreme  protrusion  is  not  desired,  but  one-fourth  of  an 
inch  or  a  little  more  will  include  the  portion  required  It 
is  obvious  that  if  the  condyle  moves  forward  and  glides  down 
the  eminentia  articularis,  and  the  incisal  portions  of  the  occlu- 
sion models  are  brought  together,  the  distal  or  molar  portion 


Fig.  66 


of  the  occlusion  models  cannot  be  in  contact;  also  that  if  a 
measure  is  taken  of  the  forward  movement  of  the  mandible 
and  of  the  separation  of  the  distal  portion  of  the  models, 
sufficient  data  is  obtained  to  reproduce  the  condyle  path. 
These  measurements  are  easily  obtained  with  Dr.  Snow  s  bite 
gauges"  (Fig.  (3()).  The  bite  gauges  consist  of  a  small  plate  ot 
metal  with  the  under  side  so  formed  as  to  be  easily  attached  to 
the  occlusal  surface  of  the  lower  model;  the  upper  surface  of 
the  bite  gauge  carries  a  blunt  metal  spud.  A  bite  gauge  is 
mounted  at  each  end  of  the  lower  model  by  wetting  the  metal 
and  pressing  it,  flush,  into  the  occlusal  surface  of  the  model. 
The  patient  is  told  that  when  the  lower  model  is  replaced 
they  are  to  protrude  the  mandible  and  close  the  jaws  until 
the  incisal  portion  of  the  models  are  in  contact.  By  this 
means  the  spud  on  top  of  the  bite  gauge  will  be  forced  part 
wav  into  the  occlusal  surface  of  the  upper  model,  thus^in  one 
operation  marking  the  forward  position  of  the  mandible  and 


138 


OCCLUSION  AND  CONTOUR  MODELS 


the  distal  separation  of  the  occlusion  models.  The  lower 
model  is  removed  from  the  mouth  and  the  bite  gauges  care- 
fully removed  so  as  not  to  distort  the  marks  made  by  them. 
At  a  future  time  these  bite  gauges  will  be  returned  to  their 
place  in  the  occlusion  models  and  establish  the  condyle  path. 
Snow  Face  Bow. — The  remaining  data  to  be  obtained  is  the 
relation  of  the  alveolar  process  of  the  maxillcB  to  the  condyles. 
This  measurement  is  obtained  by  the  Snow  face  bow,  an 
invention  of  Dr.  George  B.  Snow,  Buffalo,  N.  Y.  The  instru- 
ment consists  of  a  bow-shaped  bar  of  metal  with  a  sliding 
condyle  bar  at  each  end,  and  at  the  centre  carrying  a  universal 
clamp  and  fork  for  holding  the  occlusion  model.  A  and  B 
are  two  forms  of  the  fork  or  mouth  piece  (Fig.  07). 

Fig.   67 


Before  attempting  to  use  the  face  bow  the  outer  tubercle 
of  the  condyle  should  be  accurately  located.  By  referring 
to  the  skull  (Fig.  2,  Chapter  I),  it  will  be  seen  that  the 
glenoid  fossa  in  which  the  condyle  rests  is  just  in  front  of 
the  external  auditory  meatus,  that  it  is  enclosed  by  the 
auditory  process  at  the  back,  the  distal  end  of  the  zygoma 


OCCLUSION  AND  CONTOUR  MODELS  139 

above,  and  the  tubercle  of  the  zygoma  or  eminentia  articularis 
in  front.  This  fossa  may  be  located  by  pressing  with  the 
finger  upon  the  face  of  the  patient  about  one-half  inch  in 
front  of  the  tragus  of  the  ear,  and  at  the  same  time  requesting 
the  patient  to  widely  open  the  mouth'.  The  outline  of  the 
depression  or  fossa  should  be  accurately  located.  By  again 
referring  to  Fig.  2  it  will  be  seen  that  the  crest  of  the  tubercle 
of  the  condyle,  when  in  the  retruded  position,  is  a  little  in 
front  of  the  centre  of  the  glenoid  fossa.  As  the  mouth  is 
closed  the  tubercle  of  the  condyle  may  be  easily  felt  in  a 

Fig.  68 


spare  patient,  but  with  nmch  difficulty  in  a  very  fleshy 
patient.  However,  the  fossa  can  always  be  detected  and  the 
location  of  the  tubercle  of  the  condyle  closely  estimated. 
It  may  be  well  to  mark  the  location  of  the  tubercle  of  the  con- 
dyle upon  both  sides  of  the  face.  This  may  be  done  with  a 
very  .soft  lead  pencil  or  a  small  piece  of  court  plaster. 

Face  Bow  Technique. — The  fork  of  the  face  bow  is  removed 
from  the  clamp  and  the  i)rongs  of  the  fork  sufficiently 
warmed  to  permit  of  their  being  inserted  into  the  body  of  the 
upper  occlusion  model.    The  tail  of  the  fork  should  be  in  the 


140  OCCLUSION  AND  CONTOUR  MODELS 

median  line  of  the  face  and  parallel  with  the  imaginary 
extension  of  the  occlusal  surface  of  the  model.  A  slight 
variation  from  the  indicated  location  of  the  fork  will  be  of 
no  consequence  as  the  universal  joint  will  accommodate  itself 
to  this.  Both  occlusion  models  are  adjusted  in  the  mouth, 
and  the  patient  instructed  to  hold  them  not  hard,  but  firmly 
closed.  The  jam  nuts  of  the  condyle  bars  are  loosened  so 
that  the  bars  may  slide  freely.  The  universal  clamp  is 
opened  widely  so  that  the  bow  and  fork  may  be  easily 
adjusted.  Just  before  slipping  the  clamp  over  the  tail  of 
the  fork,  the  patient  should  be  instructed  in  the  working  of 
the  clamp  and  requested  to  set  the  clamp  when  they  are 
given  the  word.  The  clamp  is  slipped  over  the  tail  of  the 
fork,  then  the  operator  takes  his  position  directly  back  of 
the  patient,  holding  in  each  hand  an  end  of  the  bow.  The 
condyle  bars  are  adjusted  upon  the  tubercles  of  the  condyles 
as  indicated  by  the  marks  upon  the  face.  These  condyle 
bars  must  have  an  equal  pressure  upon  the  face  and  be 
advanced  an  equal  distance  through  the  bow,  which  can  be 
easily  adjusted  by  aid  of  the  grooves  upon  the  sliding  bars. 
The  universal  clamp  should  be  adjusted  without  strain  upon 
the  bow  and  fork.  The  patient  is  then  given  the  word  to 
set  up  the  clamp  screw  tightly.  The  operator  may  then 
release  one  of  his  hands  and  satisfy  himself  that  the  clamp 
is  firmly  set.  The  condyle  bars  should  again  be  inspected 
to  see  that  they  are  properly  located  and  that  the  head  of 
each  bar  is  an  equal  distance  from  the  bow.  While  the 
patient  is  firmly  holding  the  occlusion  models,  the  lips  are 
parted  and  if  the  models  are  properly  occluded  as  indicated 
by  the  median  and  four  buccal  lines,  the  models  may  be 
securely  united  by  inserting  a  four-pronged  staple  upon 
each  side.  The  condyle  bars  are  drawn  away  from  the  face, 
the  mouth  opened  and  the  united  models  attached  to  the 
face  bow  removed. 

Resume  and  Observation. — The  object  of  this  chapter  has 
been  to  differentiate  between  the  wax-bite  and  the  occlu- 
sion and  contour  models;  also  to  teach  their  use  and  how  to 
construct  them. 


OCCLUSION  AND  CONTOUR  MODELS  141 

It  should  be  observed  that  the  wax-bite  (often  called  the 
quash-bite)  is  very  limited  in  its  usefulness,  that  it  is  very 
inadequate  for  any  purpose  except  as  location  guides  for 
partial  cases.  The  quash-bite  used  for  constructing  com- 
plete artificial  dentures  belongs  to  that  class  of  short-cut 
procedures  essayed  by  charlatans  and  ignorant  persons. 
No  operator  with  an  intelligent  conception  of  the  anatomy 
and  physics  of  mastication  can  place  any  confidence  in  such 
methods.  It  is  true  that  the  quash-bite  has  been  very 
largely  used  in  the  past  and  is  too  much  used  today,  never- 
theless it  is  an  empirical  method,  and  can  never  be  asso- 
ciated with  successful  prosthesis. 

It  is  apparent  that  the  occlusion  and  contour  models  are 
the  scientific  and  only  practical  method  of  gaining  the 
necessary  data  for  constructing  useful  artificial  dentures; 
also  that  measuring  instruments  are  necessary  for  obtaining 
data  that  can  be  acquired  in  no  other  way.  In  preceding 
sections  of  this  chapter  the  Snow  face  bow  for  obtaining 
the  relation  of  the  alveolar  processes  of  the  maxillae  to 
the  condyle,  and  the  bite  gauges,  for  recording  two  points 
in  the  movement  of  the  condyle  in  its  path,  have  been 
presented. 

These  instruments  with  a  few  obsolete  ones  are  all  that 
have  been  presented  to  the  profession  prior  to  the  year  1910. 
While  the  Snow  methods  have  been  much  in  advance  of 
other  methods  there  were  still  measurements  and  means 
for  their  application  desired.  It  has  long  been  known  that 
the  pivotal  centre  of  the  temporomandibular  articulation 
in  the  open  and  shut  movement  was  not  upon  the  head  of 
the  condyle,  but  somewhere  below  the  head.  (The  Kerr 
"Articulator"  was  constructed  upon  this  fact.)  It  is  not 
believed  that  this  pivotal  centre  has  any  appreciable  effect 
upon  artificial  dentures.  However,  there  is  a  lateral  rotary 
movement  of  this  temporomandibular  articulation  that 
very  much  influences  the  stability  of  artificial  dentures  if 
long  cusp  teeth  are  used.  The  Walker-Christcnsen-Snow 
method  treated  the  condyle  path  as  a  straight  oblique  line, 
thereby  only  approximating  the  true  condition.     Excellent 


142 


OCCLUSION  AND  CONTOUR  MODELS 


results  can  be  secured  with  measurements  thus  far  obtained ; 
however,  we  should  always  strive  for  perfection  and  adopt 
improved  instruments  and  methods. 


GYSI  MEASURING  INSTRUMENTS 

Prof.  Alfred  Gys,  of  Zurich,  Switzerland,  gives  a  very 
lucid  description  of  his  instruments  for  measuring  the 
condyle  path,  the  retruded  position  of  the  condyle  and  the 
rotation  points  of  the  condyles,  beginning  with  the  January, 
1910,  number  of  the  Dental  Cosmos. 

Fio.   69 


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A,  articulator;  O,  U,  extra  bows;  G,  condyle  path  register;  H,  horseshoe  plate; 
Sch,  extra  pair  of  condyle  path  guides;  W,  angle  measure  for  condyle  path  slant; 
T,  type  plate  for  molar  groove;  S,  small  register;  St,  holder  for  register  G  (to  be  used 
when  plastering  models  to  articulator). 


The  following  quotations  and  illustrations  are  from  this 
remarkable  article  by  Prof.  Gysi : 

"According  to  Bonwill,  the  two  condyles  form  an  equi- 


GYSI  MEASi'RIXG  INSTRUMEXTS  143 

lateral  triangle  with  the  contact  point  of  the  lower  central 
incisors.  I  have  therefore  constructed  two  measuring  instru- 
ments: With  the  one  (Fig.  69,  G),  I  determine,  from  the 
forward  and  opening  movements  and  the  combination  of 
these  two,  the  form  and  direction  of  the  two  condyle  points 
of  the  triangle  in  a  vertical  plane;  with  the  other  instrument 
(Fig.  69,  S),  I  determine,  from  the  lateral  movements,  the 
path  of  the  incisor  point  of  the  triangle  in  a  horizontal 
plane. 

"From  the  registered  paths  of  these  three  points  of  the 
triangle  in  their  separate  directions,  I  can  direct  the  move- 
ment of  the  mandible  in  all  the  combinations  of  the  mas- 
ticatory movements. 

"  The  Large  Register  for  Determining  the  Slant  of  the  Con- 
dyle Path. — This  instrument  (Fig.  69,  G)  serves  to  measure 
the  path  taken  by  the  condyles  in  the  mo^•ements  of  the 
mandible.  The  important  part  of  this  instrument  consists 
of  two  lead  pencils,  which  in  every  individual  case  can  be 
placed  in  the  region  of  the  condyles  (Fig.  70). 

"  Its  attachment  to  the  mandible  is  accomplished  through 
the  horseshoe  plate  (Fig.  69,  H),  which,  with  its  points  on 
the  under  side,  is  pressed  into  the  lower  wax  model  which 
has  been  used  in  taking  the  bite  (Fig.  70).  The  whole  is 
so  well  balanced  and  weighted  that  it  will,  without  any 
further  help,  remain  firmly  in  its  position  in  the  mouth. 

"  Parallel  to  the  horseshoe  plate  (which  we  shall  consider 
as  being  in  place)  on  the  wax  model  and  on  a  line  with  the 
plane  of  occlusion,  parallel  plates  run  backward  on  both 
sides  (Fig.  70,  P),  carrying  movable  spring  lead  pencils 
in  the  region  of  the  joint  (Fig.  70,  B).  For  extreme  cases 
these  lead  pencil  holders  may  be  changed  from  the  left  to 
the  right  side,  or  moved  up  and  down  on  their  vertical  bars 
with  a  screw  (Fig.  69),  so  that  the  pencil  points  form  as 
nearly  as  possible  a  right  angle  to  the  writing  surface  of  the 
recording  card  (Fig.  70).  The  parallel  plates  with  the  lead 
pencils  may  be  adjusted  for  individual  cases  by  moving  the 
cross-bar  which  holds  them  (Fig.  70,  7'). 

"This   instrument   also    serves   as   a   compass,    like   the 


144  OCCLUSION  AND  CONTOUR  MODELS 

American  Snow  face  bow,  which  fixes  the  distance  of  the 
plaster  models  in  correct  relation  to  the  axis  of  the  joints. 

"In  order  to  find  out  the  movements  of  the  mandible  in 
different  individuals,  the  wax-bite  plates  are  prepared  in  the 
usual  manner,  except  that  the  base  plates  must  be  either  of 
modelling  compound  1.5  mm.  in  thickness,  or  of  some  other 
equally  firm  material  reenforced  in  the  usual  way  with  a 
piece  of  wire.  After  proper  attention  has  been  paid  to  all 
the  details,  such  as  securing  the  proper  fulness  of  the  wax 
models  to  insure  proper  lip  contour,  the  right  height  of  the 
plane  of  occlusion,  the  length  of  the  incisors,  the  median 
line  of  the  face,  etc.,  the  patient  is  directed  to  open  and 
close  the  mouth  several  times,  during  which  positions  of 
the  condyles  are  ascertained  by  feeling  in  the  region  of  the 
ear  where  they  move.  Then  the  positions  of  the  condyles  in 
the  resting  position  (with  the  mouth  closed)  are  found,  and 
marked  on  the  surface  of  the  skin  of  the  patient  with  a  pencil 
or  with  chalk.  Usually  the  condyles  are  found  about  one 
centimeter  in  front  of  the  tragus  of  the  ear,  in  the  direction 
of  the  outside  corner  of  the  eye  (Fig.  71).  The  horseshoe 
plate  is  then  fastened  by  its  points  to  the  lower  wax-bite 
plate  and  both  are  placed  in  the  mouth. 

"  If  some  natural  teeth  are  left  in  the  mandible,  a  horse- 
shoe plate  -vvdthout  points  can  be  used.  Some  hot  modelling 
compound  is  placed  on  the  under  side  of  this  plate  and 
pressed  over  the  teeth,  just  as  though  an  impression  were  to 
be  taken.  In  most  cases  where  there  are  natural  teeth,  it  is 
not  absolutely  necessary  to  measure  the  relations  of  the 
joints. 

"  The  condyle  path  register  is  now  attached  to  the  horse- 
shoe plate,  which  in  its  position  in  the  mouth  is  firmly  fixed 
to  the  wax-bite  plate.  The  lead  pencils  are  put  at  the  marked 
places  which  indicate  the  positions  of  the  condyles;  by 
adjusting  them  on  their  perpendicular  bars  and  through  the 
sliding  arrangement  on  the  cross-bar,  they  are  brought  close 
to  the  surface  of  the  skin. 

"The  form  and  slant  of  the  condyle  path  will  then  be 
found  by  inserting  a  piece  of  cardboard,  as  shown  in  Fig.  70, 


GYSI  MEASURING  INSTRUMENTS 


145. 


between  the  pencil  points  and  the  skin  in  the  region  of  the 
joint,  with  the  lower  edge  parallel  to  the  parallel  plates  of 
the  register.  The  latter  plates  are  again  moved  on  the  cross- 
bar until  the  pencils  are  brought  in  such  close  contact  to  the 
writing  surface  of  the  card  that  the  springs  holding  the  lead 


Fig.   70 

^^^^^^                                                                            ^1 

^^^v       ^-^     ^H 

^^^E                     ;J^| 

^^^^^^m  '  -'                 ^K^aK' ' 

^BH^^^^^H' 

jm^        ■ 

£ 

Show.s  the  method  of  determining  the  .slant  and  form  of  the  condj-le  path. 


pencils  are  under  a  pressure.  The  patient  is  directed  to  move 
the  mandible  up  and  down,  and  from  side  to  side  (chiefly 
the  latter  motion),  until  the  condyle  path  is  clearly  drawn 
on  the  surface  of  the  recording  card  (Fig.  70). 

"The  lateral  movements  of  the  mandible  show  that  the 
10 


146 


OCCLUSION  AND  CONTOUR  MODELS 


curve  first  made  by  the  opening  and  closing  movements  is 
followed  in  the  lateral  movements,  and  that  while  one  con- 
dyle moves  forward,  the  other  moves  more  or  less  backward 
(see  explanation  to  Fig.  77).  The  measuring  of  this  moving 
path  of  the  mandible  occupies  hardly  three  minutes'  time. 

"After  one  side  of  the  mandible  has  thus  been  measured, 
the  same  card  is  held  on  the  other  side,  and  the  same  pro- 
cedure is  again  followed.  After  the  measuring  is  finished, 
the  lead  pencils  are  moved  outward  by  the  sliding  arrange- 
ment on  the  cross-bar,  so  that  the  recording  card  and  the 
register  may  be  taken  away,  without,  however,  removing 


Fig.  71 


the  horseshoe  plate.  The  lead  pencils  with  their  holders 
must  not  be  moved  or  turned  on  their  vertical  bars,  as  their 
position  is  of  importance  in  attaching  the  models  to  the 
articulator,  as  we  shall  see  later.  The  wax  models  may  then 
be  taken  from  the  mouth. 

"  To  find  the  angle  of  the  registered  path  in  relation  to  the 
occlusal  plane,  a  slotted  plate  is  selected  which  corresponds 
as  nearly  as  possible  to  the  form  of  the  registered  path. 
The  plate  chosen  is  placed  directly  over  the  lead  pencil 
drawing,  so  that  the  drawn  line  can  be  seen  approximately 
parallel  to  the  sides  of  one  of  the  slots  (Fig.  73).    Press  the 


GYSI  MEASURING  INSTRUMENTS 


147 


point  of  the  axis  of  the  slotted  plate  through  the  card,  and 
then  mark  the  points  of  the  long  axis  of  the  plate  with  a  pencil. 
This  will  show  the  main  direction  of  the  path.  The  slotted 
plate  is  taken  away,  and  both  marked  points  are  joined  by  a 


Fin.   72 


Shows  the  condyle  register  with  the  horseshoe  plate  :,ii.nliiil,  i<.  nliic']  the  lower 
wax-bite  plate  is  fastened;  ST,  spring  lead  pencils;  P,  parallel  plates;  H,  horseshoe 
plate;  F,  finger  rests;  A,  place  for  inserting  holder. 

Fig    73 


\ 

^,^ 

"V 

mr.^) 

Shows  how  the  main  direction  of  the  condyle  path  is  found  by  means  of  the 
slotted  plate. 


direct  line  (Fig.  73,  left),  which  line  is  contiinied  to  the 
lower  border  of  the  card,  so  that  with  the  angle  measure  one 
can  determine  (Fig.  74)  the  acute  angle  which  this  line 
forms  with  the  lower  border  of  the  card.  As  this  lower 
border  of  the  card  is  held  (in  the  registering  of  the  path  of 


148 


OCCLUSION  AND  CONTOUR  MODELS 


the  condyles)  parallel  with  the  parallel  plates,  which  in 
turn  are  parallel  to  the  horseshoe  plate,  and  this  latter 
lies  in  the  plane  of  occlusion,  the  angle  measured  in  this  way- 
must  correspond  exactl}^  with  the  slant  of  the  path  of  the 
condyle  to  the  plane  of  occlusion. 


Fig.   74 


Shows  the  mode  of  measuring  the  angle  formed  by  the  condyle  path  and  the 
lower  border  of  the  recording  card. 


Fig.   75 


Shows  the  completed  measurements  of  the  condyle  path. 

"The  slotted  plate  chosen  is  then  placed  in  position  on 
the  articulator  and  the  known  slant  fixed  by  means  of  the 
engraved  degree  scale  on  the  joint  of  the  instrument.  Then 
proceed  in  the  same  manner  with  the  registered  condyle 
path  of  the  other  side. 


GYSI  MEASURING  INSTRUMENTS  149 

"Fig.  75  shows  a  recording  card  with  the  registered  con- 
dyle paths  of  the  right  and  left  sides,  which  have  been  meas- 
ured in  the  manner  stated.  On  the  right  side  the  condyle 
moves  in  a  slant,  the  angle  of  which  is  44  degrees  to  the  plane 
of  occlusion  (Fig.  70,  P);  on  the  left  the  measured  angle 
registers  34  degrees. 

"In  cases  where  the  curve  is  more  or  less  horizontal,  and 
the  lengthened  line  does  not  reach  the  lower  border  of  the 
card,  a  line  is  drawn  from  the  side  of  the  card  tangent  to 
the  lengthened  line  and  parallel  to  the  lower  border  of  the 
card  (Fig.  76). 


"The  objection  may  be  raised  to  my  method  of  measuring 
that  the  plane  of  occlusion  represented  by  the  wax-bite  plate 
is  not  a  fixed  point,  because  in  setting  up  the  artificial  teeth 
one  is  obliged  to  change  this  temporary  plane  of  occlusion 
according  to  circumstances. 

"This  objection,  however,  is  only  apparently  justified, 
because  in  reality  not  only  the  angle  of  the  condyle  j^ath 
to  the  temporary  plane  of  occlusion  is  obtained,  but  also  at 
the  same  time  that  to  the  alveolar  ridge,  or  to  the  mandible 
itself  as  a  whole. 

"If  the  temporary  plane  of  occlusion  is  changed,  the 
degree  of  the  angle  of  the  condyle  path  is  of  course  also 
changed  to  agree  with  the  new  plane  of  occlusion,  but  the 
relative  relations  of  the  position  of  the  mandible  itself  to 
the  condyle  path  remain  just  the  same. 


150  OCCLUSION  AND  CONTOUR  MODELS 

"1  will  now  give  an  analysis  in  detail  of  a  condyle  path 
curve  as  illustrated  in  Figs.  73  and  75. 

"Fig.  77  shows  an  enlarged  diagram  of  a  left  and  right 
condyle  path  curve,  each  of  which  is  divided  into  its  chief 
parts,  as  indicated  by  the  different  lines. 

"From  the  description  of  this  diagram  it  can  be  seen  that 
during  the  forward  and  downward  movement  of  the  one 
condyle,  the  other  runs  more  or  less  backward  horizontally. 

Fig.  77 


Analysis  of  a  right  and  left  condyle  path  as  secured  by  method  shown  in  Fig.  70: 
C,  condyle  path;  L,  left;  R,  right;  Oc,  plane  of  occlusion;  35  degrees,  angle  of  middle 
partof  path  to  plane  of  occlusion;  r,  resting  position  of  condyle;  it|i,  path  of  condyle  in 
a  right  lateral  movement;  L',  the  same  in  a  left  lateral  movement;  o,  forward  bite 
or  wide  opening  and  closing  movement. 

"The  extreme  forward  movement  and  the  opening  and 
closing  movements  may  be  divided  into  two  parts :  First,  the 
path  which  the  condyle  takes  in  a  slight  lateral  movement, 
and  second,  the  path  which  the  condyle  takes  in  its  move- 
ment on  the  eminentia  articularis,  which  is  more  or  less 
horizontal  and  finally  may  even  lead  upward. 

"As  the  last  part  of  the  path  as  represented  by  dashes  in 
Fig.  77  can  only  occur  in  extreme  lateral  or  wide  opening 
movements,  and  is  of  no  importance  in  mastication,  I 
determine  only  the  degree  of  the  angle  of  the  more  important 
middle  part  of  the  curve  to  the  plane  of  occlusion.  (In  the 
case  represented  in  Fig.  77  the  angle  registers  35  degrees.) 

"It  does  not  often  happen  that  both  condyle  path  curves 
have  the   same  form   and   slant.     Some  examples   of  the 


GYSI  MEASURING  INSTRUMENTS 


151 


differences  in  form  and  slant  between  left  and  right  condyle 
path  curves  in  the  same  individual  may  be  seen  in  Fig.  SO, 
a  to  i.  The  specimens  in  the  same  figure  from  7?^  to  q  show 
that  other  differences  may  occur,  either  in  only  one  or  in 
both  joints  at  the  same  time,  between  the  path  of  the  opening 
movement  and  the  path  of  the  lateral  movement  {n  to  q). 
For  practical  purposes  only  the  path  taken  in  the  lateral 
movement  possesses  any  value  in  the  setting  up  of  the  arti- 
ficial teeth  for  effective  mastication,  and  therefore  only  this 
angle  is  measured. 

"In  Fig.  78  I  have  compiled  a  number  of  condyle  path 
angles,  and  from  these  statistics  it  can  be  seen  that  the 
average  angle  is  about  33  degrees. 


Examples  of  Angles  of  the  Condyle  Path 

(Same  cases  individually  arranged) 


Right 

Left 

Difference 

Right 
33° 

Left 

Difference 

54° 

54° 

0° 

38° 

5° 

40° 

40° 

0° 

43° 

38° 

5° 

33° 

33° 

0° 

35° 

30° 

5° 

51° 

50° 

1° 

30° 

25° 

5° 

26° 

27° 

1° 

26° 

20° 

6° 

39° 

37° 

2° 

28° 

20° 

8° 

28° 

30° 

2° 

21° 

13° 

8° 

23° 

21° 

2° 

40° 

32° 

8° 

35° 

37° 

2° 

10° 

19° 

9° 

40° 

42° 

2° 

34° 

25° 

9° 

32° 

35° 

3° 

22° 

31° 

9° 

31° 

34° 

3° 

30° 

40° 

10° 

33° 

36° 

3° 

28° 

39° 

11° 

37° 

40° 

3° 

40° 

25° 

15° 

5° 

9° 

4° 

29° 

45° 

16° 

36° 

40° 

4° 

46° 

29° 

17° 

10" 

14° 

4° 

23° 

45° 

22° 

"The  accompanying  table  shows  the  same  cases  individu- 
ally arranged,  and  it  may  be  seen  from  it  that  in  about 
half  the  cases  there  is  a  difference  of  onl}'  about  4  degrees 


152 


OCCLUSION  AND  CONTOUR  MODELS 


between  the  right  and  the  left  side.  As  this  sHght  difference 
might  be  attributed  to  a  possible  mistake  in  measuring,  it 
can  be  truly  said  that  half  the  cases  which  I  have  measured 
had  the  same  condyle  path  angle  on  both  sides,  and  the 
other  half  showed  a  difference  of  between  5  and  22  degrees, 
averaging  about  10  degrees.  One  astonishing  case  of  excep- 
tion showed  51  degrees  on  the  right  side  and  10  degrees  on 
the  left,  a  difference  of  41  degrees. 


Diagram  of  a  number  of  condjde  path  angles.     (See  table.) 

"Fig.  79  shows  a  collection  of  condyle  path  forms,  from 
which  I  have  chosen  the  four  average  types  that  are  used  in 
my  articulator  in  the  form  of  the  slotted  plates  represented 
in  Fig.  73.  If  necessary,  other  forms  may  be  made  from 
thin  brass  plate.  These  slotted  plates  are  the  condyle  path 
guides  of  the  articulator. 

"The  Small  Register:  Instrument  for  Determining  the  Path 
of  Motion  of  the  Anterior  Triangle  Point  in  a  Horizontal  Plane. — 
The  movement  of  this  point  in  a  vertical  plane  in  the  opening 
and  closing  movement  has,  as  has  already  been  stated  in  the 
opening  chapter,  been  measured  by  Tomes  and  Dolamore,  but 
for  practical  purposes  that  has  no  value.  Only  the  path  in 
a  horizontal  plane,  which  varies  from  case  to  case,  need  be 


GYSI  MEASURING  INSTRUMENTS 


153 


determined  for  our  purposes,  as  this  alone  has  an  influence 
on  the  setting-up  of  artificial  teeth. 

"To  secure  this,  I  proceed  as  follows:  The  shaded  part  of 
the  horseshoe  plate,  as  shown  in  Fig.  82,  is  covered  with  a 


Fig.  70 


I)II1I1IMJ|I1|I) 


i 


/. 


li^Mi'jii'^^y 


The  four  average  forms  of  condyle  paths.     Examples  of  condyle  path  forms  as 
registered  in  edentulous  patients. 

thin  film  of  dark-colored  wax,  which  with  a  hot  instrument 
is  spread  to  the  thinness  of  paper. 

"A  pointed  marker  (the  small  register)  mounted  on  a 
spring  is  now  pressed  directly  over  the  median  line  of  the 
upper  wax  model  after  having  been  warmed  slightly,  and 


154 


OCCLUSION  AND  CONTOUR  MODELS 


with  a  hot  instrument  is  firmly  attached  at  the  edges.  The 
point  must  stand  out  about  one  milfimeter  over  the  occluding 
surface  of  the  wax  model  (Fig.  81). 


Fig.  80 


a 


'37« 


•'38'! 


,'43- 


40^ 


^ 


■.-.■.".'."J.Q." 


•37  ■• 


X 


51* 


e^ 


25"  .'Ho" 


■  ■AO^ 


:^- 


•431 


/  \ 


.38" 


.---30°- 


46' 


-JA" 


k 


22 


/ 


y    %- 


■5\' 


7n 


x^ 


M- 


•33^ 


■33" 


n 


+^  ^::- 


/^ 


45^ 


■2^ 


P 


'20- 


9 


'^0" 


\&' 


"  The  upper  and  lower  wax  models  are  again  placed  in  the 
mouth  and  held  in  position  by  a  Httle  tragacanth  powder,  and 


GYSI  MEASURING  INSTRUMENTS 


155 


the  patient  is  requested  to  move  the  mandible  from  side 
to  side.  The  point  of  the  marker  registers  these  movements 
on  the  coating  of  wax  on  the  horseshoe  plate.  At  first 
these  recorded  movements  are  somewhat  irregular  and 
intertwine  at  the  posterior  portion  of  the  wax-covered  part 
of  the  plate  (Fig.  82,  K),  because  in  the  beginning  the 
patient  pushes  the  mandible  too  far  forward.  Without  an 
effort  to  correct  this  improper  position  of  the  mandible,  this 
movement  is  allowed  to  continue,  and  it  will  be  seen  that 
the  mandible,  owing  to  fatigue,  will  gradually  go  back  to 
its  normal  distal  position,  and  its  path  will  be  recorded  by  a 
correct  regular  curve  {K  M  K). 


Fio.  82 


The  small  regi.-nr  Im-n  nnl 
wax  model. 


Ilorscshoo  plate  with  registered 
incisor  path. 


"The  outer  line  of  these  tangled  markings  is  the  normal 
path,  the  middle  is  the  true  median  line  and  also  the  normal 
closing  point  in  the  resting  (occlusal)  position  of  the 
mandible. 

"When  the  point  of  the  marker  is  at  M,  Fig.  82,  or  in 
resting  position  (Fig.  83),  the  usual  marks  are  made  on 
both  wax  models  at  the  notches  prepared  in  the  horseshoe 
plate  (Fig.  82,  »S'  «S')  to  show  the  proj)cr  position  of  the  models 
when  being  fa.stened  with  plaster  to  the  articulator. 

"This  instrument  is  of  great  service  in  the  use  of  any 
articulator,  because,  leaving  aside  its  special  purpose,  which 


156 


OCCLUSION  AND  CONTOUR  MODELS 


will  be  explained  later,  it  is  an  excellent  help  in  securing 
the  normal  resting  position  of  the  mandible. 

"  From  the  angle  KMK  the  relative  position  of  the  balancing 
or  rotation  points  of  the  mandible  can  be  determined  (see 
Fig.  84). 


Fig.  83 


Registering  the  incisor  path. 

"  If  both  sides  of  this  angle  are  extended  beyond  the  inter- 
secting point  (see  dotted  lines  in  Fig.  84),  the  direction  of 
the  path  of  the  lower  incisors  and  canines  during  mastication 
is  shown. 

"This  angle  of  the  incisor  path  varies  in  different  indi- 
viduals, and  therefore  the  centre  of  rotation  varies  corre- 
spondingly.    In  my  investigations  I  have  found  that  the 


GYSI  MEASURING  INSTRUMENTS 


15"i 


relative  distances  between  these  rotation  points  may  vary 
from  7  to  13  cm.  measured  by  a  line  drawn  through  the 
centre  of  the  condyles, 

"  In  some  cases  these  rotation  points  may  lie  still  farther 
away  from  the  condyles.  As  the  average  distance  (accord- 
ing to  Bonwill)  between  the  condyle  centres  is  10  cm.  the 
rotation  points  may  lie  sometimes  inside  and  sometimes 
outside  of  the  condyles.  Very  often  the  rotation  point  in 
the  same  individual  may  be  differently  situated  on  each 
side,  e.  g.,  the  one  may  lie  inside,  the  other  outside  the 
condvle. 


Fig.  84 


7crrr 


\0cr77     \Zcm 

-e- 


"The  importance  of  determining  the  exact  position  of 
these  rotation  points  can  be  best  understood  by  making 
a  drawing  like  that  in  Fig.  84  on  a  triangular  piece  of  card- 
board, and  recording  the  movements  of  the  incisor  point  of 
the  triangle  by  sticking  a  pin  successively  through  the 
balancing  i)oints  of  7,  10,  and  13  cm.,  and  with  a  sharp  lead- 
pencil  point  inserted  through   the  incisor  point  recording 


158  OCCLUSION  AND  CONTOUR  MODELS 

the  lateral  movements.    The  result  will  show  three  different 
paths. 

"Fig.  85  shows  how  both  condyles  carry  out  the  same 
movement  (in  lateral  movements)  when  the  rotation  points 
lie  outside  of  the  condyles  12  cm.  apart,  while  the  lead- 
pencil  points  attached  to  the  large  register  will  mark  paths 
in  the  opposite  direction. 

"Fig.  86  shows  how  both  the  condyles  and  the  lead-pencil 
points  of  the  large  register  will  record  opposite  paths  in 
lateral  movements  when  the  rotation  points  lie  inside  the 
condyles. 

"It  is  clear  from  these  two  illustrations  that  it  is  possible 
to  determine  the  position  of  the  rotation  points  from  the 
relations  of  the  paths  (of  the  forward  movement  on  the  right 
sides  and  the  backward  movements  on  the  left  sides  of  Figs. 
85  and  86)  recorded  by  the  registering  instrument;  but  this 
method  would  not  be  accurate  enough,  owing  to  the  short 
length  of  the  paths,  and  therefore  from  even  small  mistakes 
in  measuring  great  differences  would  arise. 

"From  the  position  of  these  rotation  points  it  is  plain  that 
they  could  not  be  considered  as  anatomically  fixed  points, 
but  rather  as  ideal  balancing  points,  and  for  that  reason 
their  existence  has  remained  unrecognized  so  long.  Walker 
recognized  their  existence  in  1896.  (See  Dental  Cosmos, 
January,  1896,  p.  34,  and  July,  1896,  p.  573.) 

"  A  balancing  point  is  therefore  the  axis  of  rotation  result- 
ing from  the  diverse  contractions  of  the  masticatory  muscles, 
and  happens  to  coincide  only  now  and  then  with  the  con- 
dyles. As  it  is  impossible  to  imitate  the  muscles  of  masti- 
cation on  an  articulator,  these  balancing  points  must  be 
substituted  by  mechanical  centres  of  rotation,  the  positions 
of  which  can  be  changed  from  case  to  case. 

"The  natural  condyles  cannot  be  considered  as  true 
rotation  points  or  axes  around  which  the  various  movements 
of  the  mandible  occur,  but  should  only  be  regarded  as  fixed 
guides  of  the  mandible  in  its  movements. 

"  It  is  therefore  not  necessary  to  try  to  imitate  the  natural 
condyles  nor  the  glenoid  fossa  on  an  articulator,  but  it  is 
necessary  to  imitate  the  muscle  movements  by  constructing 


Fig.  85 


Fig.  80 


FiK«.  85  ana  80:  «  .S7,  reKi.stering  point;  R  F,  registerinK  surface ;  PT.  soft  parts 
ovor  tho  joint;  Wp.  baianring  point;  G,  condyle;  X.  B,  moving  path  of  the  chief 
poinU  of  the  rnanrlible  and  of  the  regiftering  points  in  lateral  movements. 


160  OCCLUSION  AND  CONTOUR  MODELS 

mechanical  centres  of  rotation  (as  already  stated)  and  mech- 
anical condyle  path  guides,  as  represented  in  my  articulator 
by  slotted  plates. 

"The  importance  of  knowing  the  relative  position  of  the 
balancing  points  is  made  clear  in  Figs.  87  and  88. 

"These  balancing  points  can  be  constructed  either  geo- 
metrically with  compass  and  rule,  or  simply  by  drawing  on 
a  piece  of  cardboard  an  equilateral  triangle  with  sides  of 
about  13  cm.  in  length,  on  which  the  outline  of  the  mandible 
is  drawn,  with  the  teeth  as  in  Figs.  87  and  88.  Attach  with 
wax  small  graphite  points  between  the  central  incisors,  also 
over  the  canines  and  over  the  middle  of  each  molar.  Grind 
these  points  to  an  equal  height  with  a  piece  of  sandpaper. 
Set  the  cardboard  with  the  points  downward  on  a  piece  of 
writing  paper,  insert  a  pin  through  the  middle  of  each  con- 
dyle, and  make  lateral  masticating  motions  with  the  card- 
board, when  the  graphite  points  will  record  their  individual 
moven^ents.  If  the  same  experiment  is  made  with  the  pin 
inserted  through  the  extreme  balancing  points  of  7  and  13 
cm.  distance,  quite  different  results  will  be  obtained.  These 
two-dimensional  tracings  as  shown  in  Figs.  87  and  88  are 
not  quite  accurate;  the  angles  would  be  slightly  different 
in  a  normal  natural  case,  where  there  is  an  overbite  of 
incisors,  and  therefore  a  three-dimensional  movement. 

"In  cases  where  the  balancing  points  lie  outside  of  the 
condyles,  the  mandible  in  lateral  movements  moves  at  the 
same  time  strongly  forward.  As  the  lower  incisors  are,  how- 
ever, somewhat  hindered  by  the  overbite  of  the  upper 
incisors,  the  mandible  glides  downward  and  upward  on  the 
lingual  surfaces  of  the  upper  incisors ;  consequently  a  longer 
overbite  of  the  canines  and  higher  cusps  of  the  molars  are 
necessary,  in  order  that  the  teeth  may  not  move  too  quickly 
away  from  each  other. 

"When,  however,  the  positions  of  the  balancing  points 
lie  inside  of  the  condyles,  the  lower  incisors  move  forward 
less  obHquely  and  almost  directly  sideward,  whereby  for  some 
distance  the  contact  with  the  upper  incisors  is  secured ;  con- 
sequently the  overbite  may  be  less  and  the  cusps  of  the  molars 
may  be  lower. 


Fig.  87 


\3cm     lOcm 


\Ocm      Idem 


Fig,  88 


\Ocm      7c 


~Icm      lOc/r? 


162  OCCLUSION  AND  CONTOUR  MODELS 

"The  positions  of  the  balancing  points  are  still  more 
important  in  regard  to  the  relative  positions  of  the  upper 
and  lower  canines.  To  present  this  fact  more  clearly,  the 
path  of  the  canine  in  Fig.  87  is  presented  on  the  left  side  of 
Fig.  88,  showing  the  difference  in  the  paths  of  the  lower 
canines  according  to  whether  the  balancing  point  of  7  cm. 
or  of  13  cm.  asserts  itself. 

Fig.  89  Fig.  90 


Normal  occlusion  of  artificial  teeth.  Normal  position  in  a  lateral  movement 

when  the  correct  balancing  point  has  been 
secured. 

"  Fig.'  89,  for  example,  shows  a  side  view  of  the  canines  in 
the  normal  occlusion  as  they  are  usually  set  up  in  an  articu- 
lator for  a  practical  case.  Fig.  90  shows  the  same  in  a  lateral 
movement.  If,  however,  the  patient  has  a  different  balancing 
point,  the  canines  will  describe  another  path,  and  the  upper 
canine  will  not  pass  properly  through  the  space  between 
the  lower  bicuspid  and  canine,  but  will  rather  strike  against 
the  cusp  of  the  latter,  thus  forming  the  only  contact  point 
of  the  tooth  rows,  and  thereby  tilting  and  loosening  the 
upper  plate  (see  Fig.  91).  With  such  an  artificial  denture 
lateral  movements  are  absolutely  impossible,  and  the 
patient  in  eating  is  compelled  to  carry  on  only  up-and-down 
movements,  or  else  ultimately  the  cusps  of  the  canines  as 
well  as  those  of  the  bicuspids  must  be  ground  off,  whereby  the 
natural  appearance  and  the  usefulness  of  the  denture  is 
destroyed. 

"As  I  have  already  stated,  the  mandible  cannot  make  a 
free  lateral  movement,  being  partly  prevented  by  the  over- 
bite of  the  upper  incisors.     Therefore  the  lateral  movements 


GYSI  MEASURING  INSTRUMENTS  163 

are  combined  with  the  opening  and  closing  movements.  If  no 
overbite  were  present,  the  front  teeth  in  the  lateral  bite 
would,  after  a  short  grinding  movement,  glide  away  from  each 
other,  and  the  whole  force  of  the  masticatory  muscles  would 
rest  on  the  molars  exclusively,  so  that  the  latter  would  be 
worn  away  altogether  too  quickly.  These  conditions  may 
be  noted  in  the  ruminants  (horses,  cows,  etc.) ;  the  increased 
wearing  away  of  the  molars  is,  however,  compensated  by 
their  numerous  and  deep  enamel  folds. 

Fig.  91 


Incorrect  position  in  a  lateral   movement  when  the  balancing  point  of  the  articulator 
differs  from  the  natural  one. 

"The  upper  incisors,  because  of  their  slanting  surfaces 
on  the  Ungual  side,  have  the  important  function  of  acting 
as  the  anterior  guiding  and  gliding  plane  of  the  mandible, 
while  the  condyles  and  the  eminentia  articularis  act  as  guides 
of  the  posterior  movements  of  the  mandible.  These  latter 
guiding  planes  of  the  two  posterior  points  of  the  triangle 
have  a  slant  of  from  5  to  50  degrees,  while  the  anterior 
point  of  the  triangle  or  incisor  guide  exhibits  a  slant  of  from 
50  to  70  degrees  to  the  occlusal  plane. 

"In  edentulous  patients  it  has  been  impossible  so  far  to 
determine  the  previous  guide  angle  of  the  incisor.  I  believe, 
however,  that  this  represents  a  racial  phenomenon,  directly 
dependent  uj)on  the  facial  angle.  From  a  small  number 
of  measurements  I  have  found  that  the  angle  of  the  slant 
of  the  lingual  surfaces  of  the  incisors,  which  form  the  incisor 
guide,  amounts  to  15  degrees  less  than  the  facial  angle 
formed  by  a  line  connecting  the  outer  ear  with  the  ba.se  of 


164  OCCLUSION  AND  CONTOUR  MODELS 

the  nose,  and  a  line  connecting  the  most  prominent  part 
of  the  forehead  with  the  base  of  the  nose.  These  measure- 
ments are,  however,  too  small  in  number  and  too  superficial 
to  serve  as  full  proofs. 

"If  the  angle  of  the  guiding  surfaces  of  the  incisors  is 
determined  in  such  an  arbitrary  way,  it  is  of  no  practical 
value  in  an  artificial  denture.  For  practical  reasons,  which 
will  be  discussed  in  a  subsequent  chapter,  I  nearly  always 
choose  the  lowest  angle,  of  about  45  degrees  or  less,  for  this 
gliding  angle  of  the  incisors. 

"From  all  these  considerations  it  follows  unquestionably 
that  in  lateral  movements  the  centres  of  rotation  or  balan- 
cing points  lie  approximately  on  a  line  passing  through  the 
centre  of  the  condyle  region,  and  that  these  balancing  points 
in  different  individuals  may  lie  either  on  the  inside  or  the 
outside  of  the  condyles. 

"  As  I  shall  show  later,  the  mandible  in  opening  and  closing 
rotates  around  another  centre,  which,  however,  has  no 
infiuence  in  the  setting  up  of  the  teeth  for  articulation,  and 
therefore  need  not  be  considered  in  the  construction  of  an 
articulator.  In  the  Walker  articulator  this  opening  axis  can 
be  attached,  and  is  used  when  the  plane  of  articulation  is 
to  be  lowered  or  raised.  In  the  Kerr  articulator  the  true  axis 
of  rotation  on  opening  is  permanently  fixed  on  the  articulator. 
In  my  articulator  the  ordinary  axis  for  opening  and  closing 
movements  is  used — as  it  has  no  influence  on  the  slant  of 
the  condyle  path — in  the  same  way  as  in  Walker's  and 
Christensen's  articulator. 

"From  these  observations  it  follows  that  in  the  construc- 
tion of  an  articulator  the  following  points  should  be  con- 
sidered : 

"  1.  An  individually  changeable  slant  of  the  condyle  path. 

"  2,  An  individually  changeable  form  of  the  condyle  path. 

"  3.  A  changeable  incisor  guide. 

"4.  Two  individually  changeable  balancing  or  rotation 
points. 

"5.  The  incisor  guide  must  not  change  the  slant  of  the 
condyle  path;  the  slant  of  the  condyle  path  must,  therefore, 
be  independent  of  the  opening  movement." 


CHAPTER    V 

ARTICULATORS  AND  ANTAGONIZORS 

Definition.^ — Articulator  is  a  name  applied  to  apparatus 
of  many  designs.  Of  these  many  designs  it  may  truly  be 
said  that  a  few  are  good,  that  a  few  others  are  bad,  but  that 
the  most  of  them  are  indifferent.  Unfortunately  the  name 
is  a  misnomer,  but  it  is  so  universally  used  that  it  seems  a 
useless  expenditure  of  time  to  more  than  explain  the  anomaly. 
The  term  is  used  in  the  anatomical  sense,  and  means  "a 
joint,"  hence  the  instrument  can  only  rightly  be  termed  an 
articulator  because  of  its  hinge  joint,  not  because  of  the 
operation  for  which  it  is  designed.  The  instrument  is  used 
to  assemble  artificial  teeth  in  occlusion,  and  they  should  be 
in  antagonization.  The  operation  for  which  the  instrument 
is  intended  is  to  occlude  and  antagonize  the  teeth  and  not 
to  articulate  the  teeth,  as  is  usually  stated,  for  teeth,  both 
natural  and  artificial,  can  articulate  only  upon  their  proxi- 
mate mesial  and  distal  surfaces;  but  not  upon  their  occlusal 
surfaces.  The  name  "articulation"  for  assemblage  of  the 
teeth  is  a  misnomer,  therefore  it  is  absurd  to  name  the  instru- 
ment in  conformity  with  the  misnamed  operation. 

Under  the  general  term  "articulator"  two  distinct  types  of 
instruments  are  included,  the  simple  hinge  joint  class  called 
articulator  (Fig.  92),  and  the  class  which  make  a  pretence 
of  imitating  the  temporomandibular  articulation  called 
anatomical  articulator.  Hereafter  in  this  book  when  the 
hinge-joint  type  is  referred  to  it  will  be  called  occlusion 
frame,  and  when  the  other  type  is  meant  it  will  be  called 
the  antafjonizor. 

Occlusion  Frame. — An  occlusion  frame  is  a  dentist's 
apparatus  to  secure  the  open  and  shut  arrangement  of 
artificial  teeth. 


166 


ARTICULATORS  AND  ANTAGONIZORS 


Aniagonizor. — An  antagonizor  is  a  dentist's  apparatus  to 
secure  anatomical  and  mechanical  arrangement  of  artificial 
teeth. 

Fig.  92 


Upper  plate 


Hinge  pin 


Lower  plate 


History. — Guerini  gives  credit  for  the  original  invention 
of  this  device  to  J.  B.  Gariot  about  1805.  Many  forms  of 
the  apparatus  have  since  been  devised,  a  few  of  which  are  of 
historical  interest  because  they  denote  professional  thought 
and  endeavor. 

August  28,  1840,  Daniel  T.  Evans,  of  Philadelphia, 
obtained  a  patent  for  an  apparatus  having  slot  and  pin 
joints,  by  means  of  which,  as  he  expressed  it  in  his  speci- 
fications, "the  lower  plate  is  allowed  a  motion  at  the  joints 
similar  to  that  which  is  admitted  by  the  condyloid  processes 
of  the  Hving  subject"  (Fig.  93). 

In  1858  Dr.  W.  G.  A.  Bonwill,  of  Philadelphia,  invented 
his  instrument.  He  presented  the  instrument  and  his 
studies  of  anatomical  antagonization  before  the  American 
Dental  Association  at  Niagara  Falls,  N.  Y.,  in  1864.     Dr. 


HISTORY 


167 


Bonwill  may  be  justly  called  the  father  of  anatomical  antag- 
onization  and  antagonizors  because  of  the  volume  of  research 
work  and  writing  he  did  upon  the  subject.  Undoubtedly 
his  genius  has  inspired  all  later  work  in  this  field  of  endeavor 
(Fig.  94). 

In  1889  Dr.  Richmond  S.  Hayes,  of  East  Bloomfield,  N.  Y., 
received  a  patent  for  an  antagonizor  which  embodied  at 


Fig.  93 


least  one  new  feature.  He  probably  was  the  first  to  attempt 
to  reproduce  the  downward  motion  of  the  condyle.  Prof. 
Gysi  says,  speaking  of  the  "forward  and  downward  slope": 
"This  fact  had  previously  been  noted  by  two  anatomists — 
Luce,  of  Boston  (1889),  and  Count  Spec  (1890) — but  their 
work  remained  unknown  to  dentists  for  some  years."     It 


168  ARTICULATORS  AND  ANTAGONIZORS 

will  be  noticed  that  the  earlier  date  given  by  Prof.  Gysi  is 
the  same  as  of  the  patent  paper  of  Dr.  Hayes. 

The  Walker  antagonizor  (Fig.  95):  Dr.  George  B.  Snow, 
of  Buffalo,  in  his  paper  pubHshed  in  the  Dentist's  Magazine, 
July,  1907,  says:  "In  1896  Dr.  W.  E.  Walker,  then  of  Pass 
Christian,  Miss.,  now  of  New  Orleans,  obtained  a  patent  upon 
an  antagonizor  constructed  in  much  the  same  manner  as  the 

Fig.  94 


Bonwill,  but  with  adjustable  joints  for  imitating  the  direction 
of  the  condyle  path.  Dr.  Walker  is  the  first  one  who  clearly 
recognized  the  fact  that  there  was  a  considerable  variation 
in  the  inclination  of  movements  of  the  condyle  upon  the 
eminentia  articularis.  He  obtained  another  patent  upon 
an  instrument  by  which  the  inclination  of  the  condyle  path 
could  be  ascertained.  This  he  called  a  'facial  cHnometer.' 
But  he  also  lost  sight  of  the  second  condition  of  the  problem, 


HISTORY  169 

the  correct  location  of  the  casts  in  the  antagonizor.  Dr. 
\Yalker  made  a  close  study  of  his  subject,  and  his  papers, 
published  in  the  Cosmos  for  1896  and  1897,  are  well  worth 
reading.  They  are,  in  fact,  nearly  exhaustive  so  far  as  they 
go,  and  he  is  entitled  to  great  credit,  much  more  than  he  has 
received  for  their  presentation." 

Fig.  95 


In  1899  Dr.  A.  De  Witt  Gritman,  then  of  Buffalo,  but  now 
of  Philadelphia,  and  Dr.  George  B.  Snow  introduced  the 
Gritman  antagonizor  and  the  Snow  face  bow. 

In  1901,  in  Aslis  Quarterly,  and  the  Cosmos  for  October, 
190.J,  Prof'.  Carl  Christenson  describes  his  antagonizor.  In 
the  paper  previously  referred  to  Dr.  Snow  says:  "He 
(Prof.  Christenson)  showed  at  that  time  his  simple  and  prac- 
tical method  of  ascertaining  the  inclination  of  the  condyle 
path,  and  transferring  it  to  the  antagonizor,  thus  taking  the 


170 


ARTICULATORS  AND  ANTAGONIZORS 


last  step  necessary  for  the  full  solution  of  the  problem  of  the 
correct  antagonization  of  full  dentures.  But  he  did  not 
recognize  the  importance  of  correctly  locating  the  casts  in  the 
antagonizor,  and  in  the  one  which  he  constructed,  which 
much  resembles  that  of  Dr.  Walker,  he  unfortunately 
designed  it  so  that  the  casts  cannot  be  placed  near  enough 
to  the  joints." 

In  the  Transactions  of  the  Odontological  Society  of  Great 
Britain,  1903,  J.  B.  Parfit  described  his  antagonizor  with 
its  curved  condyle  path  constructed  for  each  case.  This 
instrument  required  that  the  ascertained  condyle  path  for 
each  individual  case  be  cut  out  of  a  sheet  of  metal  and 
clamped  to  the  jaw  of  the  antagonizor. 


Fig.  96 


In  1907  Dr.  George  B.  Snow  introduced  the  New  Century 
Antagonizor  (Fig.  96).  This  instrument  is  built  upon  the 
Unes  of  the  Gritman.  The  frame  is  higher  arched  and 
therefore  more  open  at  the  back  than  its  predecessor.  It 
has  each  bow  secured  with  two  set  screws.  Beginning  with 
January,  1911,  the  instrument  is  to  be  provided  with  an 
extra  pair  of  bows,  the  lower  of  which  will  be  extra  long  and 
the  upper  bayonet-shaped,  thus  accommodating  any  thickness 
of  casts.  The  straight  upper  bow  has  a  sleeve  for  marking 
its  position,  so  that  it  may  be  removed  and  returned  at  will. 
The  position  of  the  lower  bow  is  registered  by  the  plaster 


G  YSI  A  X  TA  GOXIZOR 


171 


securing  the  lower  cast.  It  has  straight  slotted  adjustable 
condyle  paths,  and  metal  spuds  for  obtaining  the  inclination 
of  the  paths.  The  central  spiral  clamping  spring  is  ettectual 
and  convenient.  There  is  an  extension  of  the  slot  pm  or 
supporting  the  face  bow.  The  face  bow  accessory  ot  this 
instrument  has  been  described  (Chapter  IV).  It  is  a  simple, 
well-constructed,  and  effectual  instrument.  It  reproduces 
most  of  the  essential  movements  of  the  mandible.  It  cer- 
tainly has  no  equal  save  one,  the  elaborate  instrument  ot 
Prof."^  Gvsi. 


Fig.  97 


Gysi  Antagonizor.-At  the  time  of  writing  this  chapter  the 
author  has  had  no  practical  experience  with  the  Gysi  instru- 
ments, but  from  the  written  description,  and  inspection 
of  them,  he  is  confident  the  new  instruments  ofler  great 
'L  ibilities  for  the  prosthetist.  The  following  is  P-f^Gysi  s 
description  of  the  antagonizor  as  presented  m  the  February, 

1910,  JJentfd  Cosmos:  ,., 

"This  antagonizor  (Fig.  09,  A,  and  l^>g-^,.97),  l^ke 
all  others,  consists  of  a  movable  upper  part  (Hg  9/,  U) 
and  a  fixed  lower  part,  U.    To  the  upper  part  the  bayonet- 


172  ARTICULATORS  AND  ANTAGONIZORS 

shaped  bow,  o,  is  attached  and  secured  by  screws,  S.  An 
extra  straight  bow  (Fig.  69)  can  be  inserted  if  prefer- 
able. To  the  lower  part  a  straight  bow  is  attached  and 
secured  by  screws,  *S.  An  extra  bow  (Fig.  69,  U)  can  be 
attached  having  a  base  that  is  1^  cm.  higher.  With  these 
four  bows  six  different  combinations  can  be  effected  to 
correspond  to  the  height  of  the  plaster  casts,  thus  saving 
much  time  in  their  preparation  for  the  antagonizor.  The 
bows  should  be  oiled  and  pushed  as  far  into  the  antagonizor 
as  they  will  go,  so  that  should  it  be  necessary  for  any  reason 
to  remove  them  together  with  the  casts  from  the  antagonizor, 
they  can  be  easily  and  accurately  placed  in  their  former 
positions. 

"To  the  upper  bow  an  adjustable  supporting  pin,  St,  is 
attached,  which  rests  on  the  narrow  end  of  the  small  plate, 
T,  of  the  lower  bow.  On  this  narrow  end  of  the  lower  bow  is 
attached  an  inclined  plane,  E,  on  which  the  supporting  pin 
moves  upward  in  the  side  movements.  The  supporting  pin 
should  always  rest  at  the  foot  of  this  inclined  plane.  This 
inclined  plane  forms  the  incisor  guide,  and  serves  on  the 
antagonizor  as  a  substitute  for  the  overbite.  Up  to  the 
present  time  the  artificial  incisors,  attached  with  wax  to  the 
trial  plates,  have  taken  the  place  of  this  incisor  guide.  This 
was  a  most  uncertain  guide,  especially  in  warm  weather. 
For  practical  reasons,  which  will  not  be  further  discussed, 
this  inclined  plane  is  attached  to  the  lower  part  of  the 
antagonizor  instead  of  to  the  upper  part,  just  as  all  antagon- 
izors  have  a  fixed  lower  and  a  movable  upper  part,  entirely 
contrary  to  the  natural  relations,  but,  as  is  well  known, 
answering  the  same  purpose. 

"As  the  supporting  pin  acts  as  a  guide  to  the  height  of 
the  bite,  it  is  placed  in  front  of  the  incisors,  because  it  is 
only  here  that  a  true  and  secure  support  can  be  obtained. 
If  this  supporting  pin  interferes  with  the  setting  up  of  the 
incisors,  it  can  be  removed  until  the  latter  are  placed  in 
position. 

"File  marks  (Fig.  97,  F)  can  be  made  on  the  supporting 
pin,  so  that  there  is  at  all  times  a  guide  to  show  that  the 


GYSI  ANTAGONIZOR  173 

height  of  the  bite  has  not  been  changed  in  the  setting  up  of 
the  teeth. 

"The  placing  of  this  supporting  pin  in  front  of  the  incisors 
offers  the  further  ach'antage  that  the  antagonizor  is  quite 
unobstructed  at  the  back,  so  that  the  lingual  surfaces  of 
the  teeth  are  clearly  visible  and  can  easily  be  reached  with 
the  fingers  and  wax  spatula.  This  is  important,  in  that  it 
permits  of  the  correct  antagonization  of  the  lingual  surfaces 
of  the  teeth. 

"The  most  important  function  of  this  supporting  pin  and 
the  inclined  plane  consists  in  the  prevention  of  the  wrong 
downward  movement  of  the  upper  part  of  the  antagonizor 
produced  in  all  antagonizors  up  to  this  time  when  repro- 
ducing lateral  movements. 

"The  upper  bow,  o,  is  connected  with  the  upper  part  of 
the  antagonizor  by  a  hinge  joint,  so  that  in  the  setting  up  of 
the  artificial  teeth  opening  and  closing  movements  can  be 
made  that  are  independent  of  the  true  joint  movement; 
consequently  the  two  condyle  parts  of  the  triangle  can  be 
combined  exactly  and  precisely  with  the  incisive  part  of  the 
triangle  in  such  a  way  that  all  unnatural  movements  are 
impossible.  In  this  manner  the  downward  movement  of 
the  mandible  combines  with  the  forward  movement  in  the 
direct  forward  and  lateral  movements.  This  combined 
movement,  which  has  long  been  recognized,  is  for  the  first 
time  accurately  reproduced  by  the  antagonizor. 

"The  upper  and  lower  parts  of  the  antagonizor  are  con- 
nected through  the  real  joint,  G,  which  permits  of  the 
lateral  movements.  Two  springs,  F,  automatically  bring 
the  two  parts  back  to  their  normal  positions. 

"The  joint  is  formed  by  the  fork,  (j,  of  the  lower  part  of 
the  antagonizor,  the  prongs  of  which  pass  through  the 
E-shaped  part  of  the  upper  half  and  receive  the  slotted  plate, 
Sy.  The  fork  y  rotates  and  with  the  slotted  plate  can  be 
fixed  by  the  screw,  5,  at  an  angle  of  from  0  to  50  degrees. 

"The  two  identical  slots  in  the  slotted  plate  which  receive 
the  prongs  of  the  fork  (j  corresjjond  in  form  to  the  path  which 
the  condyles  take  in  their  movement  during  mastication. 


174  ARTICULATORS  AND  ANTAGONIZORS 

"To  be  quite  exact,  a  number  of  different  forms  of  slotted 
plates  should  be  kept.  From  my  long  experience,  however 
I  have  found  that  the  two  average  forms  are  quite  sufficient, 
and  if  the  artificial  teeth  are  placed  in  the  exact  position 
necessary  to  secure  the  full  value  of  the  gradations  of  these 
two  condyle  path  forms,  the  result  is  most  satisfactory.  If 
a  special  form  for  every  case  is  thought  necessary,  as  advo- 
cated by  Campion  and  Parfitt,  it  can  be  easily  and  quickly 
sawed  out  of  thin  brass  plate  and  placed  on  the  antagonizor. 

"The  pin,  st,  found  on  the  slotted  plate  serves  to  bring 
the  latter  into  its  proper  place,  and  should  always  be  placed 
in  the  hole  provided  for  it  in  the  middle  of  the  E-shaped 
joint. 

"In  order  to  change  the  slotted  plate,  the  binding  screw, 
5,  is  first  loosened,  then  the  prongs  of  the  fork  g  are  turned 
to  a  vertical  position,  which  will  allow  the  plate  to  slide  over 
the  head  of  the  binding  screw.  With  the  prongs  in  the  same 
position  another  plate  can  be  put  on  and  fixed  at  the  desired 
angle.  This  is  accomplished  by  placing  the  index  of  the 
slotted  plate  at  the  required  degree  on  the  engraved  scale, 
W,  in  the  E-shaped  joint. 

"The  two  small  supporting  pins,  D  D,  at  the  back,  with 
the  large  supporting  pin,  St,  form  a  secure  triangle  which  is 
not  to  be  found  in  any  other  antagonizor.  This,  together 
with  the  solid  cast  pieces,  prevents  any  looseness  or  any 
springiness,  and  thus  insures  the  possibility  of  true  and 
exact  work. 

"The  small  supporting  pins,  D D,  in  the  slotted  upper 
part,  0,  can  be  moved  sideways.  They  rest  on  the  transverse 
piece  of  the  lower  part,  on  which  is  an  engraved  scale  to  indi- 
cate the  positions  of  the  pins.  As  the  positions  of  these 
supporting  pins  are  determined  by  the  incisor  path  these 
scales  are  only  of  value  when  two  or  more  full  upper  and 
lower  dentures  are  to  be  made  at  the  same  time,  when  the 
different  positions  of  these  pins  can  be  noted  on  the  plaster 
casts.  For  unmeasured  cases  and  partial  dentures  the  pins 
are  placed  at  the  average  position  of  10  cm.,  forming  a 


GYSI  ANTAGONIZOR  175 

Bonwill  triangle  with  the  average  distance  of  10  cm.  between 
the  condyles. 

"The  rear  supporting  pins  form  the  true  balancing  or 
rotation  points  in  the  lateral  movements  of  the  mandible. 
They  can  lie  from  7  to  13  cm,  apart,  and  even  more,  in  spite 
of  the  fact  that  the  condyles  in  adults  on  an  average  seldom 
lie  farther  apart  than  10  cm.  These  balancing  points,  as 
stated  before,  do  not  exist  anatomically,  but  are  the  result 
of  the  various  muscle  contractions  that  move  the  mandible, 
and  are  its  true  rotation  points  during  lateral  masticatory 
movements. 

"When  in  trying  in  dentures  it  is  found  that  the  antago- 
nization  is  not  correct  in  lateral  movements  (which  cannot 
occur,  if  my  incisor  register  is  used)  a  correction  can  easily 
be  made  by  attaching  a  piece  of  cardboard  or  thin  metal 
plate  with  wax  under  one  of  the  supporting  pins  until  the 
proper  antagonizing  position  is  secured,  when  the  teeth  can 
be  re-antagonized. 

"When  the  antagonization  is  faulty  because  the  mandible 
has  been  pushed  too  far  forward  in  taking  the  bite,  it  is 
corrected  in  the  same  manner  as  in  other  antagonizors,  by 
drawing  out  the  upper  bow  to  the  distance  necessary  for 
correction. 

"With  the  rear  supporting  pins  placed  at  the  average 
position  of  10  cm.  and  the  slant  of  the  condyle  path  fixed 
at  the  average  angle  of  30  degrees,  the  antagonizor  will  be 
found  of  great  value  for  all  partial  dentures,  bridges,  and 
even  for  single  crowns;  because,  when  the  natural  lateral 
movements  are  reproduced,  the  proper  height  of  the  cusps 
can  be  accurately  determined,  and  porcelain  facings  can  be 
so  placed  that  the  liability  to  breakage  because  of  improper 
occlusion  or  antagonization  will  be  reduced  to  a  minimum. 

"For  small  casts  the  high-base  bow  (Fig.  69  U,)  can  be 
used,  together  with  the  inverted  bayonet-shaped  bow, 
making  the  space  between  the  bows  so  small  that  thick  plaster 
foundations  will  not  be  necessary. 

"The  great  value  of  this  antagonizor  consists  in  the  fact 
that  complete  upper  and  lower  dentures  can  be  made  in 


176  ARTICULATORS  AND  ANTAGONIZORS 

exact  conformity  to  the  individual  relations  of  the  joints, 
and  that  when  the  average  positions  of  both  scales  are  used 
it  is  an  anatomically  perfect,  stable,  and  handy  antagonizor 
for  all  partial  dentures,  crowns,  and  bridges-. 

"When  the  antagonizor  is  used  without  the  help  of  the 
measuring  instruments,  it  is  important  to  place  all  casts 
so  that  the  occlusal  plane  is  exactly  parallel  to  the  table  on 
which  the  antagonizor  stands,  as  the  degree  scales  are 
founded  on  a  corresponding  horizontal  plane.  It  is  also 
important  to  have  the  front  of  the  casts  at  an  equal  distance 
of  10  cm.  from  the  rear  supporting  pins,  thus  forming  a 
Bonwill  triangle." 

MOUNTING 

How  Mounted. — The  two  types  of  instruments  under  con- 
sideration are  for  distinct  operations.  The  antagonizors  may 
be  used  as  an  occlusion  frame,  but  the  occlusion  frame 
cannot  be  used  as  an  antagonizor.  The  operation  of  occlusion 
is  a  simple  one,  while  that  of  antagonization  is  complex, 
and  includes  occlusion  as  one  of  its  factors. 

The  occlusion  frames  are  designed  to  hold  the  plaster  casts 
in  a  fixed  position,  but  for  convenience  of  mounting  the 
teeth  upon  either  cast,  the  other  should  be  removed  suffi- 
ciently to  give  finger  room  for  manipulation;  hence,  the 
instrument  is  provided  with  a  hinge-joint,  thus  permitting 
removal  without  loss  of  relationship.  As  the  instrument  is 
designed  to  hold  the  casts  in  a  fixed  position,  it  can  make 
no  difference  in  what  position  the  casts  are  mounted  in  the 
frames,  so  long  as  the  position  is  convenient  for  manipulation. 
Usually  the  incisoit  section  of  the  casts  are  placed  at  the 
front,  but  in  some  partial  cases  it  may  convenience  the  work- 
man to  place  the  bicuspid  section  to  the  front;  the  relation- 
ship of  the  casts,  however,  will  be  the  same. 

The  antagonizors  being  designed  to  hold  the  casts  and 
mounted  teeth  in  many  positions,  it  is  necessary  that  the 
casts  shall  be  definitely  and  accurately  located,  therefore 
specific  instruction  is  required  for  occlusion  frames  as  a 


MOUNTING  177 

class,  and  each  antagonizor;  however,  of  the  antagonizors 
the  Snow  and  Gysi  only  will  be  further  considered. 

Mounting  upon  Occlusion  Frames. — The  plaster  casts  and 
wax-bite,  or  occlusion  and  contour  models,  as  may  be  had, 
are  assembled  and  united  with  a  little  melted  wax.  These 
are  placed  upon  the  lower  part  of  the  occlusion  frame,  the 
upper  part  is  adjusted  with  the  set  screw  so  that  it  will  be 
just  free  of  the  upper  cast,  and  the  set  screw  is  fixed  with 
the  jam  nut  (Fig.  92).  The  casts  are  united  to  the  frame 
with  a  soft  mix  of  plaster;  however,  if  the  plaster  casts  have 
been  standing  a  few  hours  so  as  to  become  dry,  they  should 
be  saturated  with  water  just  before  mixing  the  attaching 
plaster.  Some  of  the  soft  mixed  plaster  is  placed  upon  a 
slightly  oiled  surface;  any  convenient  substance,  as  glass, 
marble,  metal,  or  wood,  or  a  piece  of  paper,  may  be  placed 
upon  the  work  bench,  and  the  plaster  placed  upon  it.  The 
occlusion  frame  containing  the  casts  is  placed  on  the  soft 
plaster  and  firmly  pressed  into  place.  The  upper  portion 
of  the  occlusion  frame  is  raised,  soft  plaster  placed  upon 
the  upper  cast,  and  the  raised  portion  of  the  frame  pressed 
firmly  into  it.  The  soft  plaster  may  be  smoothed  by  trowel- 
ling with  the  plaster  spatula  (Fig.  27).  If  the  casts  have 
been  made  unnecessarily  thick  it  may  be  necessary  to  trim 
them  down,  otherwise  it  may  be  difficult  to  adjust  them  in 
the  occlusion  frames. 

Mounting  upon  the  Snow  Antagonizor. — The  antagonizor 
is  prepared  ioT  the  case  b\'  adjusting  the  set  screw  and 
making  firm  its  jam  nut,  so  that  the  bows  are  parallel  to 
each  other.  The  bows  are  then  adjusted  to  give  the  necessarj^ 
space  to  insert  the  assembled  casts  and  models.  This  is 
accomplished  by  sliding  the  lower  bow  either  up  or  down  and 
using  either  the  straight  or  bayonet-shaped  upper  bow,  as 
may  be  required  to  accommodate  the  case.  The  lower  cast 
should  be  so  trimmed  that  the  occlusal  surfaces  of  the  wax 
models  shall  be  parallel  with  the  bows.  The  case  being 
mounted  without  the  face  bow,  the  assembled  casts  and 
models  should  be  centrally  located,  with  the  portion  repre- 
.senting  the  mesial  incisal  angle  of  the  lower  central  incisor 
12 


178  ARTICULATORS  AND  ANTAGONIZORS 

teeth  four  inches  from  either  condyle  joint.  The  assemblage 
is  then  united  with  plaster  as  described  for  occlusion  frames. 
Mounting  with  the  Face  Bow. — The  set  screw  with  its  jam 
nut  having  been  fixed  as  described  in  the  preceding  paragraph, 
the  assembled  casts,  occlusion  and  contour  models,  and  face 
bow%  as  described  in  Chapter  IV,  are  ready  for  mounting 
in  the  antagonizor.  The  condyle  bars  of  the  face  bow  are 
pushed  in  to  their  limit  and  made  fast  with  their  jam  nuts. 
The  head  of  each  condyle  bar  has  a  depression  which  fits 
over  the  extended  slot  pin.  The  heads  of  the  condyle  bars 
are  adjusted  to  the  antagonizor  by  springing  the  face  bow 
sufficient  to  permit  the  heads  to  slip  over  the  slot  pins.  The 
lower  cast  rests  on  the  lower  bow;  however,  the  cast  must 
not  be  attached  to  the  lower  bow  until  the  occlusal  surface 

Fig.  98 


of  the  occlusion  model  is  parallel  with  the  horizontal  portion 
of  the  lower  bow.  This  relationship  of  cast  and  bow  may  be 
secured  either  by  trimming  the  cast  (which  is  rarely  neces- 
sary), or  by  pushing  in  or  pulling  out  the  lower  bow.  The 
lower  bow  being  adjusted,  it  is  secured  with  its  set  screws. 
Either  the  straight  or  bayonet-shaped  upper  bow  is  adjusted 
as  may  be  necessary  to  clear  the  upper  cast.  The  casts  are 
then  made  fast  to  the  bows  with  plaster  as  previously 
described  (Fig.  98).  The  plaster  luting  having  thoroughly 
hardened,  the  face  bow  is  removed.  The  remaining  step 
is  to  secure  the  inclination  of  the  condyle  path.  Loosen  the 
condyle  clamps  so  the  slotted  condyle  bars  may  move  freely, 
unhook  the  spiral  spring,  readjust  the  bite  gauges.  (See 
Chapter  IV.)     The  bite  gauges  being  adjusted  in  both  wax 


MOUNTING 


179 


models  and  the  incised  portion  of  the  wax  models  in  contact, 
the  slotted  condyle  bars  must  assume  their  respective  posi- 
tions, when  they  are  firmly  clamped  (Fig.  99).  The  bite 
gauges  are  removed  and  the  spiral  spring  attached  (Fig.  100). 


Fig.  99 


Fig.  100 


Mounting  upon  the  Gysi  Antagonizor. —  "When  the  wax 
models  have  been  constructed  and  the  relations  of  the  joints 
have  been  securefl  the  wax  models  are  placed  on  their  respec- 
tive cast.s.    The  latter  are  then  placed  in  correct  relation  to 


180 


ARTICULATORS  AND  ANTAGONIZORS 


each  other  by  means  of  the  marks  on  the  wax  models,  without 
removing  the  horseshoe  plate.  After  it  has  been  ascer- 
tained that  the  point  of  the  small  register  rests  exactly  in 
the  centre  of  the  recording  wax  surface  of  the  horseshoe 
plate,  it  is  pushed  up  and  turned  into  its  resting-place  so  that 
it  may  not  separate  the  models  owing  to  its  spring.  The 
models  can  be  slightly  fastened  with  a  Httle  hot  wax,  and  held 


together  temporarily  with  a  rubber  band.  The  large  register 
is  then  attached  to  the  horseshoe  plate,  and  with  the  aid  of 
the  holder  (Fig.  69,  St)  the  whole  is  placed  in  position  as 
shown  in  Fig.  101.  When  the  graphite  points  of  the  large 
register  are  placed  exactly  at  the  axis  of  the  fork  g,  Fig. 
97,  the  casts  are  in  correct  relation  to  the  joint. 

"The  plaster  casts  must  be  cut  until  they  will  go  into 
the  proper  positions.    This  is  important  in  case  it  is  found 


MOUNTING 


181 


necessary,  after  trying  in  the  teeth,  to  raise  or  lower  the 
height  of  the  bite. 

"^Yhen  the  casts  have  been  attached  the  large  register 
may  be  taken  away,  leaving  the  horseshoe  plate  in  its 
place.  The  slotted  plates  presenting  the  condyle  paths  are 
placed  in  position  and  set  at  the  desired  angle. 


"  Lateral  movements  are  then  made  and  the  rear  support- 
ing pins  are  adjusted  so  that  the  point  of  the  small  register 
follows  the  angle  K  M  K,  Fig.  82,  on  the  horseshoe  plate.  In 
this  manner  the  true  balancing  points  of  the  mandible  are 
determined  and  fixed  on  the  antagonizor  (Fig.  1<)2). 

"The  front  supporting  pin  is  then  placed  in  position  with 


182 


ARTICULATORS  AND  ANTAGONIZORS 


the  point  at  the  foot  of  the  incHned  plane,  thus  fixing  the 
height  of  the  bite.      The  horseshoe  plate  is  taken  away, 


some  wax  being  added  to  the  lower  model  to  fill  in  the 
space  that  had  been  occupied  by  the  plate.  The  small 
register  is  also  taken  away  (Fig.  103)." 


CHAPTER    VI 

RUBBER  AND  VULCANITE^ 

Rubber. — India  rubber  or  caoutchouc. 
Vulcanite. — A    chemical    compound    of    caoutchouc    and 
sulphur. 

CAOUTCHOUC 

History.— Caoutchouc  is  a  native  Indian  name.  India 
rubber  is  a  name  given  the  material  because  its  early  use 
in  Europe  was  to  remove  black  lead  pencil  marks  from  paper. 
Dr.  Priestley,  the  distinguished  discoverer  of  oxygen,  men- 
tions this  use  in  a  publication  of  1770.  Caoutchouc  must 
have  been  known  in  America  at  a  very  early  period,  because 
balls  made  from  the  gum  of  a  tree,  lighter  and  bounding 
better  than  the  wind-balls  of  Castile,  are  mentioned  by 
Herrera  when  speaking  of  the  amusements  of  the  natives 
of  Haiti,  in  his  account  of  the  second  voyage  of  Columbus. 
In  a  book  published  in  Madrid,  1615,  Juan  de  Torquemada 
mentions  a  tree  which  yields  it  in  Mexico,  describes  the 
mode  of  collecting  the  gum,  and  states  that  it  was  made 
into  shoes.  More  exact  information  was  furnished  by  a 
French  Academician,  who  visited  South  America  in  1735. 
While  the  Indians  used  it  more  than  three  hundred  years 
ago  for  water  bottles  and  gum  shoes,  it  was  only  used  ni 
the  United  States  and  Europe  for  erasing  pencil  marks, 
until  about  1820,  when  it  was  applied  to  waterproofing 
cloth.  As  caoutchouc  became  hard  and  brittle  in  cold 
weather  and  sticky  in  hot  weather,  many  experiments  were 

1  The  JiiHtorj',  physical  and  chomif-al  proportios  of  rubber  and  vulcanite  are  taken 
fron.  the  Author's  chapter  in  Turner's  An.erican  Text-Hook  of  Prosthetic  Dentistry. 


184  RUBBER  AND  VULCANITE 

made  to  overcome  this  objectionable  quality,  which  resulted 
in  the  discovery  of  vulcanite  in  1843. 

Physical  Properties. — Caoutchouc  is  the  dried  milky  juice 
of  various  trees  and  plants.  A  similar  gum  capable  of  vul- 
canization can  be  obtained  from  the  common  milkweed  and 
other  plants  of  temperate  climates,  but  it  is  ouly  commer- 
cially profitable  from  certain  trees  in  the  tropics.  The 
Brazilian,  or  Para  (a  shipping  port  on  the  Amazon  river) 
caoutchouc  is  the  product  of  several  species  of  Siphonia 
(nat.  ord.  Euphorbiacese),  chiefly  Siphonia  elastica.  Bates 
says  that  this  tree  is  not  remarkable  in  appearance;  in  bark 
and  foliage  it  is  not  unlike  the  European  Ash,  but  the  trunk, 
like  that  of  all  forest  trees,  shoots  up  to  an  immense  height 
before  throwing  off  branches.  The  India  rubber  produced 
in  New  Granada,  Ecuador,  and  Central  America  is  obtained 
from  Castilloa  elastica;  that  of  East  India  from  the  beauti- 
ful glossy-leaved  Ficus  elastica,  now  a  common  ornamental 
plant  in  conservatories;  that  of  Borneo  from  Urceola  elas- 
tica; and  that  of  West  Africa  from  several  species  of  Landol- 
phia  and  also  Ficus. 

After  the  trees  are  tapped,  the  juice  is  first  received  in 
clay  basins,  and  then  is  solidified  in  various  ways — as  by 
spreading  it  out  in  thin  layers  and  evaporating  in  the  sun 
or  by  the  aid  of  artificial  heat;  or  the  emulsion  is  coagulated 
by  the  leaves  of  a  kind  of  vine — a  method  used  in  Central 
America — which  gives,  however,  a  product  inferior  to  that 
obtained  by  evaporation.  The  evaporated  product  is  known 
as  "biscuit."  The  fresh  juice  has  the  consistency  of  cream, 
is  yellow,  miscible  with  water,  but  not  with  naphtha  or  other 
solvents  of  ordinary  rubber;  its  specific  gravity  is  1.02  to 
to  1.41;  the  yield  of  the  gum  is  about  30  per  cent.  Pure 
caoutchouc  is  devoid  of  odor  and  is  nearly  white;  it  has  the 
specific  gravity  of  0.915.  The  finest  quality  of  caoutchouc 
is  that  from  Brazil  (Para),  which  has  the  least  impurities; 
the  other  South  and  Central  American  kinds  are  of  medium 
quality;  East  India  rubber  ranks  next,  while  the  African 
rubber  is  quite  inferior. 


CAOUTCHOUC  185 

Commercial  India  rii})ber  is  a  dark,  tough,  fibrous  sub- 
stance, possessing  elastic  properties  in  the  highest  degree. 
At  the  freezing  point  of  water  it  hardens  and  largely  loses 
its  elasticity.  The  gum  is  insoluble  in  water  or  alcohol, 
and  is  not  acted  upon  by  alkalies  or  acids  except  when  the 
latter  are  concentrated  and  heat  is  applied.  It  is  soluble  in 
ether,  chloroform,  bisulphide  of  carbon,  naphtha,  petroleum, 
benzol,  and  the  essential  oils,  and  in  many  of  the  fixed  oils 
by  the  aid  of  heat.  Caoutchouc  melts  at  a  temperature  of 
250°  F.  and  does  not  again  resume  its  former  elastic  state; 
at  600°  F.  it  volatilizes  and  undergoes  decomposition. 

Purifjdng. — In  the  manufacture  of  India-rubber  the  first 
operation  is  the  purification  of  the  crude  material.  The 
impure  rubber  is  cut  into  minute  shreds  and  is  washed  by 
powerful  machinery  immersed  in  water,  which  releases  the 
solid  impurities.  The  washed  gum  is  then  placed  on  iron  trays 
and  dried  in  a  room  heated  by  steam.  The  material  then 
undergoes  a  process  of  kneading  under  very  heavy  rollers, 
which  causes  the  adhesion  of  its  various  pieces  to  each  other 
and  ultimately  yields  a  mass  or  block  of  India  rubber  so  com- 
pact that  all  air-holes,  other  cells,  and  interstices  disappear. 

Chemistry  of  Caoutchouc.^ — India  rubber,  as  is  well-known, 
is  the  product  of  the  coagulation  of  the  milky  juice  of 
a  large  number  of  trees,  creepers,  and  shrubs.  The  com- 
mercial article  can  hardly  be  expected  to  be  homogeneous, 
and  still  less  a  pure  product  in  the  chemical  sense.  Besides 
accidental  impurities  of  sand  and  fragments,  it  contains  a 
greater  or  less  amount  of  oily  and  resinous  matter,  which 
varies  greatly  e\'en  in  the  same  brand  of  rubber.  Para 
rubber  contains  from  1  to  2  per  cent.;  Logus  rubber  from 
3  to  7  per  cent.;  Borneo  rubber  from  6  to  21  per  cent.;  and 
African  Flake  may  contain  as  high  as  04  per  cent.  Lascelles- 
Scott  gives  the  composition  of  a  brand  of  unnamed  origin: 

'  The  writer  uses  as  his  authority  for  this  paragraph  and  the  subsequent  ones  upon 
the  Chemistry  of  Vulcanite,  "The  Chemistry  of  India  Rubber,"  by  Carl  Otto  Weber, 
Ph.D.,  published  by  Charles  Griffin  &  Co.,  Limited,  London;  J.  B.  Lippincott  Com- 
pany. Philadelphia,  1903. 


186  RUBBER  AND  VULCANITE 

Per  cent. 

India  rubber  (gum) 37.13 

Albumin 2.71 

Resins 3.44 

Essential  oils Traces. 

Sugar 4.17 

Mineral  matter 0.23 

Water 52.32 

The  pure  Para  gum  consists  of  soluble  and  insoluble 
portions,  the  latter  averaging  about  3.5  per  cent.  The 
soluble  portion  has  a  formula  of  CioHie,  and  is  the  portion  with 
which  the  sulphur  combines  to  form  vulcanite.  The  formula 
for  the  insoluble  portion  is  CsoHesOio. 


VULCANITE 

History. — Charles  Goodyear/  of  New  Haven,  Conn.,  dis- 
covered the  process  of  curing  or  vulcanizing  India  rubber 
in  1843.  Thomas  Hancock,  of  England,  has  been  credited 
with  making  this  discovery  contemporaneously;  but  his 
own  writiugs  state  that  he  had  seen  small  samples  of  Good- 
year's  work,  and  that  after  much  experimenting,  he  pro- 
duced the  same  thing;  so  the  priority  of  the  discovery 
undoubtedly  belongs  to  Goodyear. 

On  January  30,  1844,  a  patent  was  granted  to  Charles 
Goodyeai  for  making  soft  or  flexible  rubber  that  would  resist 
the  action  of  the  usual  solvents  of  caoutchouc,  and  would  not 
be  affected  by  cold  or  heat  if  the  temperature  were  not  raised 
above  the  vulcanizing  point.  The  mixture  he  preferred  was 
caoutchouc,  25  parts;  sulphur,  5  parts;  and  white  lead,  7 
parts.    This  produced  soft  vulcanite. 

The  process  of  making  hard  rubber  was  patented  by 
Nelson  Goodyear  May  6,  1851.  His  formula  consisted  of 
one-half  pound  of  sulphur  to  a  pound  of  caoutchouc  and 
one-half  pound  of  any  one  of  a  long  list  of  earthy  substances. 

1  This  historical  sketch  of  vulcanite  is  made  up  largely  from  the  monograph,  "In- 
structions in  Vulcanite,"  by  Prof.  E.  Wildman,  M.D.,  D.D.S.,  Philadelphia,  Samuel 
S.  White,  1867. 


VULCANITE  187 

A  patent  was  granted  to  Charles  Goodyear,  Jr.,  "For 
improvement  in  plates  for  artificial  teeth,"  dated  March  4, 
1855.  He  says:  "The  best  compound  I  believe  to  be  one 
pound  of  India  rubber  or  gutta-percha  (or  of  the  two  com- 
bined in  suitable  proportions)  with  a  half  pound  of  sulphur, 
together  with  a  suitable  quantity  of  coloring  matter.  To 
obtain  a  suitable  color,  I  mix  with  caoutchouc  or  gutta- 
percha, vermilion,  oxide  of  zinc,  oxide  of  iron,  or  any  coloring 
substance  that  will  stand  the  necessary  degree  of  heat  with 
the  action  of  sulphur.  This  compound,  after  having  been 
molded,  is  subjected  to  heat  for  about  six  hours,  and  in  so 
doing  I  gradually  raise  the  heat  to  about  230°  F.,  say  in 
half  an  hour,  and  then,  unless  there  be  a  considerable  quantity 
of  foreign  matter  present,  the  heat  may  be  raised,  quickly 
as  may  be,  to  about  295°  F.;  otherwise,  I  raise  the  heat  more 
slowly  and  keep  the  compound  at  about  that  temperature  for 
the  remainder  of  the  six  hours,  and  then  allow  the  whole  to 
cool  down,  when  the  process  will  be  completed." 

A  patent  was  granted  in  June,  1857,  to  H.  H.  Day  for 
vulcanizing  very  thick  pieces  of  rubber.  To  accomplish 
this,  he  mixes  with  the  matter  prepared  for  vulcanization 
a  substance  that  will  prevent  its  becoming  spongy  or  cellular, 
by  absorbing  the  sulphur  gases  as  fast  as  generated.  The 
material  which  he  proposed  to  employ  for  this  purpose 
is  ordinary  fire  clay,  but  other  substances  capable  of  absorb- 
ing the  gas  may  be  employed. 

In  Austin  G.  Day's  specification  we  find  some  interesting 
remarks  upon  the  nature  of  rubber  compounds.  In  contra- 
distinction to  Nelson  Goodyear's  hard  and  inflexible  sub- 
.stance,  he  claims  his  compound  to  be  a  hard,  but  highly  elastic 
material  obtained  by  a  process  differing  from  that  of  N. 
Goodyear's  in  the  length  of  time,  in  the  degree  of  heat,  in 
the  proportion  of  the  ingredients,  and  in  the  mode  of  equal- 
izing the  temperature. 

Day's  comj)osition  is  one  pound  of  purified  Para  rubber 
and  one-half  pound  of  sulphur. 

lie  remarks:  "In  the  vulcanizing  process  there  is  elimi- 
nated during  the  whole  operation  a  constant  discharge  of 


188  RUBBER  AND  VULCANITE 

sulphuretted  hydrogen  and  other  sulphuretted  gases,  which 
must  have  means  of  escape  through  the  pores  of  the  mass 
while  being  vulcanized.  By  my  present  improved  manage- 
ment of  the  heat  in  vulcanizing,  by  raising  it  very  gradually, 
step  by  step,  to  the  highest  point,  I  am  enabled  to  vulcanize 
pieces  of  an  inch  or  more  in  thickness  with  great  uniformity 
and  perfection.  A  mixture  containing  earthy  matter  may 
be  vulcanized  in  much  shorter  time  than  one  consisting  of 
caoutchouc  and  sulphur  alone,  and  yet  be  solid,  owing  to  the 
earthy  matter  facilitating  the  escape  of  the  gases  generated 
in  its  substance  during  the  process.  At  the  same  time  such 
compositions  are  destitute  of  elasticity  and  flexibility. 
For  a  piece  five-eighths  of  an  inch  thick,  the  time  required 
for  vulcanizing  is  thirteen  and  one-half  hours : 

It  is  held  at 275°  F.,  for  6  hours. 

Then  raised  to  and  held  at 280°  F.,  for  3  hours. 

Then  raised  to  and  held  at 290°  F.,  for  2  hours. 

Then  raised  to  and  held  at 295°  F.,  for  2  hours. 

Then  raised  to  and  held  at      ...      .  ...  300°  F.,  for  |  hour. 

Composition  of  Vulcanite  for  Artificial  Dentures. — As  the 
formulae  of  the  various  makes  of  rubber  are  "trade  secrets" 
of  the  manufacturers,  our  knowledge  is  limited  to  the 
general  specifications  of  patent  papers  and  the  writings  which 
detail  the  experiments  of  Prof.  Wildman  and  others. 

Both  the  soft  pliable  and  the  hard  flexible  vulcanite  are 
used  in  the  construction  of  dentures.  The  essential  com- 
ponents of  vulcanite  are  caoutchouc  and  sulphur,  the  ratio 
varying  according  to  the  use  for  which  the  product  is  de- 
signed. All  other  ingredients  are  for  coloring  or  to  cheapen 
the  product. 

The  soft  pliable  variety  used  in  dentistry  is  known  as 
velum  rubber,  because  its  most  important  use  is  for  vela 
for  cleft  palates.  It  contains  sulphur  to  the  extent  of  about 
one-fifth  of  the  weight  of  the  gum.  Hard  vulcanite,  some- 
times called  ebonite,  contains  by  weight  one-half  as  much 
sulphur  as  caoutchouc. 


VULCANITE 


189 


Some  of  the  formulas  siven  by  Prof.  Wildman  are: 
Dark  Brown 

^       i  I-  ....     48  parts 

Caoutchouc 

„   ,   ,  24  parts 

Sulphur 

Red 

Caoutchouc t!^^? 

Sulphur 24pars 

.,.                                                                                                ...  36  parts 

Vermilion 

Dark  Pink 

Caoutchouc _    P 

OIL  ....  24  parts 

Sulphur on         t 

White  oxide  of  zinc JU  p.arts 

.,•  ...  10  parts 

vermilion 

Grayish  White 

Caoutchouc „,  ^^  , 

„   ,   .  24  parts 

Sulphur OR        i 

White  oxide  of  zinc 90  parts 

Black 

Caoutchouc ^ 

c.   1   L  ....  24  parts 

Sulphur 9A         f 

Ivory  black  or  drop  black "^^  P^"^ 

Jet  Black 

Caoutchouc P^ 

c  ,  ■.                                                                                                  ...      24  parts 
Sulphur ,o        *„ 

Ivorj'  black  or  drop  black 4«  P'*''^^ 

If  pure  caoutchouc  is  burned,  there  should  be  but  about 
3  per  cent,  of  dark  ash  remaining.  Sulphur  and  vermilion 
(mercuric  sulphide)  leave  no  ash,  hence  the  percentage  of 
ash  from  rubber  containing  these  materials  should  be  less 
than  3  in  the  ratio  of  the  amount  of  these  materials 
to  the  caoutchouc.  Some  rubbers  leave  as  high  as  60  per 
cent,  of  ash.  It  would  be  reasonable  to  suppose  that  the 
strength  would  be  reduced  in  ratio  to  the  amount  of  the  ash, 
but  this  is  not  true,  as  the  pure  gum  and  sulphur  produce  the 
strongest  vulcanite;  the  red  and  black  are  nearly  the  same 
strength,  although  the  black  rubber  will  leave  a  much  larger 
ash  than  r(;d,  because  the  coloring  matter  is  animal  charcoal 
composed    largely    of    phosphate    and    car})onate    of    lime, 


190  RUBBER  AND  VULCANITE 

while  the  mercuric  sulphide  would  be  entirely  volatilized. 
The  oxide  of  zinc  and  other  earthy  matter  in  the  pink  and 
white  rubbers  have  a  very  deleterious  effect  upon  the  flexi- 
bility and  tenacity  of  the  vulcanized  rubber,  so  much,  in  fact, 
that  these  light  colored  vulcanites  are  not  one-fourth  as 
strong  as  the  brown,  red,  or  black. 

Physical  Properties  of  Vulcanite. — Vulcanite  is  hard, 
flexible,  and  horn-like  in  texture.  Dr.  George  B.  Snow 
gives  the  specific  gravity  of  a  specimen  of  black  vulcanite 
as  1.1974,  and  that  of  the  same  piece  before  vulcanizing  as 
1.1333.  The  specific  gravity  varies,  as  it  is  much  affected 
by  the  coloring  matter,  and  is  also  increased  by  the  temper- 
ature and  time  of  vulcanization.  Caoutchouc  expands 
upon  heating.  Dr.  Snow  says:  "Rubber  expands  by  heat 
more  rapidly  than  any  other  solid  body.  Its  rate  of  expansion 
at  ordinary  temperatures,  from  70°  to  90°  F.  is  over  six 
times  that  of  iron,  about  five  times  that  of  brass,  and  nearly 
four  times  that  of  zinc,  which  is  the  most  susceptible  to 
expansion  by  heat  of  any  of  the  metals.  Its  rate  of  expansion 
is  known  to  increase  as  the  temperature  rises,  but  it  has  not 
been  definitely  determined."  In  vulcanizing  soon  after 
chemical  action  begins  (248°  F.),  expansion  ceases  and  con- 
traction commences,  the  latter  being  much  affected  by  the 
contained  foreign  matter,  by  a  high  or  low  temperature, 
and  by  a  long  or  short  time  of  vulcanization.  Its  increased 
specific  gravity  is  due  to  this  contraction. 

The  usual  solvents  of  caoutchouc  have  but  little  action 
upon  vulcanite,  and  no  agent  which  can  be  tolerated  in  the 
mouth  has  any  action  upon  it.  It  is  susceptible  of  a  high 
polish.  It  is  very  opaque,  and,  therefore,  does  not  imitate 
well  the  appearance  of  the  mucous  membrane.  It  is  a  very 
poor  conductor  of  thermal  and  electrical  changes,  in  con- 
sequence of  which  it  is  not  conducive  to  the  health  of  the 
tissues  upon  which  it  is  worn.  It  is  porous,  although  this 
condition  is  invisible  to  the  eye.  It  absorbs  the  secretions 
of  the  mouth,  even  though  the  rubber  has  been  perfectly 
vulcanized,  and  when  improperly  vulcanized  it  becomes  so 
saturated  with  decomposing  secretions  that  it  is  exceedingly 


VULCANITE  191 

offensive.  Great  care  should  be  used  in  vulcanizing  rubber 
that  is  to  be  worn  in  the  mouth,  and  the  patient  should  be 
thoroughly  instructed  in  cleansing  it. 

New  rubber  can  be  added  to  old  vulcanite  by  reheating; 
hence  vulcanite  dentures  can  be  easily  repaired.  It  is 
unnecessary  to  add  a  solution  of  rubber  to  vulcanite  to  aid 
in  its  repair,  as  the  solvent  has  no  action  upon  the  vulcanite, 
only  leaving  a  thin  layer  of  soft  rubber  to  penetrate  the 
pores  of  the  vulcanite,  a  result  better  accomplished  by  heat 
and  pressure. 

Chemistry  of  Vulcanization. — \\ilcanization  consists  of  the 
chemical  iniion  of  caoutchouc  and  sulphur,  probably  pro- 
ducing a  series  of  compounds  having  the  formula  CioHieSi  for 
the  highest  combination,  and  CiooHieoS  for  the  lowest,  with 
a  series  from  the  lowest  to  the  highest. 

Vulcanization  can  be  brought  about  either  by  the  cold  or 
the  hot  process,  and  by  using  with  the  latter  either  the  dry 
or  the  wet  method.  The  essential  requisite  is  to  secure  the 
union  of  the  sulphur  with  the  polyprene  (CioHie). 

The  cold  process  is  by  the  use  of  sulphur  monochloride, 
and  is  only  suitable  for  very  thin  layers  of  rubber,  being, 
therefore,  not  applicable  for  dental  use.  An  attempt  has 
been  made  to  sell  to  the  profession  office  rights  for  the  use 
of  a  porcelain  enamel  for  facing  vulcanite  dentures.  This 
method  was  based  upon  the  cold  vulcanization  process. 
While  the  results  were  an  improvement  upon  ordinary 
pink  rubber,  the  product  lacked  the  translucent  effect  of 
fused  porcelain,  its  durability  was  uncertain,  and  the  process 
was  long  and  tedious. 

Mr.  Weber  in  the  work  previously  referred  to,  says:  "We 
turn  our  attention  first  to  the  question  of  the  general  action 
of  sulphur  upon  India  rubber  at  high  temperatures.  The 
sulphur  bath  method  might  appear  from  several  points  of 
view  the  most  suitable  method  of  studying  this  question,  but 
after  a  number  of  attempts  I  abandoned  it  in  favor  of  the 
method  of  subjecting  carefully  prepared  homogeneous 
mixtures  of  l*ara  rubber  with  a  definite  amount  of  sulphur 
to  the  action  of  heat.    Again  in  this  case  we  have  the  choice 


192  RUBBER  AND  VULCANITE 

of  several  methods  of  heating,  but  the  one  of  heating  pieces 
of  Para  mixture  of  uniform  thickness  to  vulcanizing  tem- 
peratures when  immersed  in  water  appeared  to  me  the  most 
satisfactory,  as  it  involves  the  minimum  of  loss  of  sulphur 
by  evaporation. 

"The  experiments  were  carried  on  with  strips  cut  from  a 
calendered  sheet,  3  mm.  in  thickness — a  mixture  of  100 
parts  of  Para  rubber  with  10  parts  of  pure  precipitated  sul- 
phur. These  strips  were  vulcanized  in  a  phosphor-bronze 
digester. 

"The  digester  is  provided  with  a  thermometer  tube 
(thermometer  in  mercury),  a  pressure  gauge,  and  a  blow-off 
valve.  In  the  digester  a  porcelain  beaker  is  suspended  so 
that  it  is  clear  of  the  bottom.  The  digester  is  filled  to  about 
one-quarter  of  its  capacity  with  water;  the  beaker  is  com- 
pletely charged  with  water,  and  a  number  of  the  strips  to 
be  experimented  upon  immersed  in  it.  The  digester  is  then 
closed,  rapidly  heated  to  the  required  temperature,  and 
maintained  thereat,  either  by  carefully  adjusting  the  gas 
burner,  or  by  means  of  some  form  of  thermo-regulator.  At 
regular  intervals  one  of  the  strips  is  withdrawn  after  blowing 
off  steam  and  rapidly  opening  the  digester,  which  is  then 
immediately  closed  again  to  continue  the  series.  The  time 
error  caused  by  these  successive  withdrawals  does  not 
exceed  four  minutes  per  sample.  Of  course,  the  water  lost 
by  the  blow-off  steam  is  from  time  to  time  made  up  with 
boiling  water. 

"  The  strips  thus  withdrawn  are  marked,  and  subsequently 
cut  into  very  fine  threads,  which  are  freed  from  every  trace 
of  uncombined  sulphur  by  extraction  with  acetone  in  a 
Soxhiet  extractor.  The  greatest  care  was  employed  to  render 
this  operation  perfect,  every  sample  being  subjected  to  a 
three  days'  continuous  extraction.  The  extracted  samples 
were  dried  in  a  current  of  carbonic  acid  in  the  water  oven, 
and,  until  analysis,  were  preserved  in  carefully  stoppered 
glass  tubes. 

"About  one  gram  of  each  of  these  samples  was  used  for 
analysis.      The   sulphur   determinations   were   all,   without 


VULCANITE  193 

exception,  carried  out  by  Cariiis'  method,  as  the  results  by 
the  much  simpler  and  more  expeditious  method  proposed  by 
Henriques  were  found  to  be  liable  to  an  error  approaching 
0.1  per  cent,  in  magnitude.  In  this  manner  the  following 
results  were  obtained: 

Vulcanization  of  Para  Rubber 

Temperature  of  vulcanization. 

Duration  of  120°  C.  125°  C.  130°  C.  135°  C.          140°  C. 

vulcanization.  S.%  S.%  S.%  S.%                 S.% 

30njins.  0.71  0.71  0.99  1.76 

60      "  1.18  1.32  1.44  2.17 

90      "  1.31  1.67  2.04  2.36 

120      "  1.62  1.91  2.32  3,92               ;' 

150   "        4.02 

180  •'  1.78  2.11  2.94  4.18      C 

240   "  1.93  2.22  5.00  5.50 

300  "  2.25  2.35  5.27  6.74 

360   "  2.60  3.80  5.82  6.88 

420   "  3.71  4.04  6.04  6.97 

480   "  3.94  4.31  6.33  7.13 

"These  figures  amply  suffice  to  demonstrate  indisputably 
the  fact,  even  quite  recently  again  denied,  that  the  vulcani- 
zation of  India  rubber  with  sulphur  involves  the  chemical 
combination  of  these  two  substances,  at  any  rate  so  far  as 
the  vulcanization  of  Para  rubber  is  concerned. 

"That  different  brands  of  India  rubber  behave  very 
differently  in  the  vulcanization  process  is  a  well-known 
fact,  but  what  we  know  at  this  moment  respecting  the 
composition  and  chemical  relationship  of  these  different 
brands  entitles  us  to  assume  that,  although  their  behavior 
under  vulcanization  may  not  be  identical  with  the  Para 
rubber,  it  will  be  more  or  less  closely  analogous  to  it." 

Following  this,  Mr.  Weber  gives  a  tabulation  of  his  experi- 
ments with  L'pper  Congo,  Beni  River,  Ceara,  and  Borneo 
rubber  for  the  same  duration  of  vulcanization  and  for  125°  C. 
and  135^  C.    He  then  sums  up  these  experiments  thus: 

"The  extremely  interesting  results  here  tabulated  remove 
all  doubt  that  the  vulcanization  of  India  rubber  is  a  chemical 
13 


194  RUBBER  AND  VULCANITE 

process  resulting  in  the  formation  of  a  polyprene  sulphide. 
The  rate  at  which  the  sulphur  enters  into  combination  with 
the  India  rubber  hydrocarbon  (polyprene)  is  characteristic 
for  each  brand  of  India  rubber.  Some  of  the  above  series 
were  repeatedly  investigated,  always  with  the  same  result. 

"There  arises  now,  of  course,  at  once  the  question  as  to 
the  nature  of  the  process  by  which  sulphur  enters  into  com- 
bination with  the  polyprene,  whether  the  polyprene  sul- 
phide or  sulphides  formed  are  addition  or  substitution 
products.  Certainly  what  we  already  know  respecting  the 
chemical  nature  of  India-rubber,  leads  us  to  infer  that  the 
vulcanization  process  consists  essentially  in  the  formation 
of  an  addition  product  of  sulphur  and  polyprene.  This 
assumption,  however,  requires  support  in  view  of  the  fact 
that  quite  a  number  of  writers,  from  Payen  to  most  of  the 
recent  authors,  declare  that  vulcanization  is  accompanied 
by  the  evolution  of  hydrogen  sulphide,  thereby  implying 
that  the  process  is  a  substitution,  and  not  an  addition 
process.  Indeed,  most  of  the  recent  authors  on  this  subject 
state  this  in  so  many  words.  We,  shall,  therefore  have  to 
subject  this  point  to  a  careful  examination. 

"  Assuming  the  compound  of  polyprene  and  sulphur,  which 
indisputably  forms  in  the  vulcanization  process,  to  be  a 
substitution  product,  it  follows  with  absolute  necessity 
that  for  each  32  parts  of  sulphur  combining  with  the  poly- 
prene, we  must  obtain  34  parts  of  hydrogen  sulphide.  Now, 
in  the  process  of  vulcanization  as  practically  carried  out,  we 
obtain  on  an  average,  a  product  containing,  say,  2.5  per 
cent,  of  combined  sulphur.  Consequently  the  vulcanization 
of  one  ton  of  India  rubber,  on  the  above  assumption,  would 
be  bound  to  yield  very  nearly  60  pounds  of  hydrogen  sul- 
phide, or  approximately  18,000  liters.  Considerifig  that 
in  a  number  of  factories  the  amount  of  India  rubber  vul- 
canized daily  largely  exceeds  one  ton  in  weight,  we  should 
expect  to  find  the  vulcanizing  rooms  of  these  factories 
reeking  with  gas.  As  a  matter  of  fact,  however,  there  is 
scarcely  ever  a  trace  of  this  gas  to  be  discovered  in  the 
rubber  works'  atmosphere,  and  the  very  rare  cases  in  which 


VULCANITE  195 

its  presence  becomes  noticeable  may  always  be  considered 
as  an  indication  of  something  having  gone  wrong. 

"  In  the  vulcanization  of  '  hard  rubber'  goods  (ebonite 
vulcanite)  faint  but  distinct  traces  of  hydrogen  sulphide 
are  generally,  perhaps  always,  observable,  but  they  could 
not  be  ascribed  to  the  vulcanization  process  proper- — the 
combination  of  polyprene  with  sulphur — which  process,  if 
it  consisted  in  the  substitution  of  hydrogen  for  sulphur, 
should  cause  a  perfectly  torrential  evolution  of  hydrogen 
sulphide,  seeing  that  'hard  rubber'  contains  at  least  20  per 
cent,  of  combined  sulphur. 

"It  is,  therefore,  certain  that  if  hydrogen  sulphide  forms 
at  all  in  the  vulcanizing  process,  its  amount  is  utterly  inade- 
quate to  support  the  assumption  that  the  process  of  vulcani- 
zation is  a  substitution  process. 

"Laboratory  experiments  on  this  question  lead  to  exactly 
the  same  conclusion.  If  the  experiments  are  carried  out 
with  technically  i)ure  Para  rubber  under  conditions  abso- 
lutely' precluding  the  escape  of  any  gaseous  product  of  the 
reaction,  very  minute  traces  of  hydrogen  sulphide  may  some- 
times be  observed;  but  in  a  considerable  number  of  carefully 
devised  experiments  with  highly  purified  Para  rubber  no 
hydrogen  sulphide  at  all  could  be  detected. 

"If,  on  the  other  hand,  the  'insoluble'  part  of  India-rubber 
is  mixed  with  sulphur,  and  this  mixture  is  subjected  to  a 
vulcanizing  temperature,  say  about  135°  C,  a  considerable 
evolution  of  hydrogen  sulphide  takes  place,  due  to  the  for- 
mation of  a  substitution  product  of  this  insoluble  body, 
CsoIIcsOio,  with  sulphur.  This  substitution  process  certainly 
proceeds  much  slower  than  the  vulcanization  process  of 
India  rubber  (polyprene).  Under  the  same  conditions  of 
tem[)erature  and  the  time  under  which  polyprene  forms  a 
vulcanization  product  containing  4  per  cent,  of  sulphur,  the 
above-named  insoluble  constituent  forms  a  substitution 
product  containing  at  most  0.7  per  cent,  of  suli)hur. 

"  From  these  facts  we  are  justified  in  drawing  the  following 
conclusions: 


196  RUBBER  AND  VULCANITE 

"I.  The  India  rubber  hydrocarbon,  polyprene  C10H16, 
combines  with  sulphur  without  evolution  of  hydrogen 
sulphide.  The  vulcanization  process  of  India  rubber  is, 
therefore,  an  addition  process. 

"2.  The  insoluble  constituent  of  India-rubber,  which 
forms  only  an  insignificant  proportion  of  the  technical  prod- 
uct, not  exceeding  5  per  cent,  of  the  total,  combines  with 
sulphur  under  vulcanizing  conditions  at  a  very  slow  rate, 
with  evolution  of  hydrogen  sulphide  and  with  the  formation 
of  a  substitution  product. 

"The  above  conclusively  settles  the  question  regarding 
the  general  chemical  aspect  of  the  vulcanization  process, 
but  it  confronts  us  with  the  further  question  respecting  the 
quantity  of  sulphur  combining  with  India-rubber  in  this 
process,  as  well  as  the  more  intimate  structure  of  the  com- 
pound thus  formed." 

Interesting  and  instructive  as  the  work  of  Mr.  Weber  is, 
the  limits  of  this  chapter  will  not  permit  us  to  follow  him  in 
detail,  but  only  to  give  his  conclusions. 

"The  process  of  vulcanization  consists  in  the  formation  of 
a  continuous  series  of  addition  products  of  polyprene  and 
sulphur,  with  probably  a  polyprene  sulphide,  C100H160S,  as 
the  lower,  and  C100H160S20  as  the  upper  limit  of  the  series. 
Physically  this  series  is  characterized  by  the  decrease  of 
distensibihty,  and  the  increase  of  rigidity,  from  the  lower 
to  the  uper  limit.  Which  term  of  the  above  series,  that  is, 
which  degree  of  vulcanization  is  produced,  is  in  every  case 
only  a  function  of  temperature,  time,  and  the  proportion  of 
sulphur  present. 

"As  a  chemical  reaction  the  vulcanization  process  is  not 
influenced  by  the  physical  state  of  the  India  rubber  colloid; 
but  the  physical  state  of  the  India  rubber  colloid  while 
under  vulcanization  largely  determines  the  physical  con- 
stants of  the  vulcanization  product." 

From  the  above  we  conclude  that  dental  vulcanite  is 
essentially  polyprene  disulphide  having  the  symbol  CioHieS" 
which  contains  32  per  cent,  of  combined  sulphur. 


VULCANITE  FOR  ARTIFICIAL  DENTURES        197 


ADVANTAGES    AND    DISADVANTAGES    OF    VULCANITE 
AS  A  BASE  FOR  ARTIFICIAL  DENTURES 

Advantages. — 1.  It  is  easy  of  manipulation;  it  can  be 
molded  into  any  form,  and  it  becomes,  upon  proper  vulcani- 
zation, very  strong,  tough,  and  flexible.  It  is  repaired  with 
equal  ease. 

2.  It  is  the  lightest  of  all  substances  used  in  the  mouth; 
its  specific  gravity  is  from  1.15  to  1.50,  while  aluminum,  the 
lightest  metal  suitable  for  use  in  the  mouth,  has  a  specific 
gravity  of  from  2.5  to  2.7. 

3.  It  is  inexpensive,  both  as  to  cost  of  material  and  labor 
in  construction,  thus  bringing  it  within  the  reach  of  patients 
unable  to  afford  metal  plates. 

4.  There  is  no  material  with  which  contours  can  be  so 
easily  and  perfectly  restored. 

Disadvantages. — 1.  It  is  a  very  poor  conductor.  It  pre- 
vents the  proper  radiation  of  heat  from  the  mucous  mem- 
brane over  which  it  is  placed,  thereby  leading  to  excessive 
resorption  of  the  hard  tissue  and  lowering  the  vitality  of 
the  soft  tissue,  in  consequence  of  which  they  are  more 
subject  to  the  action  of  irritants. 

2.  It  is  a  porous  material,  and  because  this  condition  is 
greatly  exaggerated  by  improper  vulcanization,  it  affords 
lodgement  for  bacteria,  the  products  of  which  are  very  strong 
irritants  to  the  soft  tissue. 

The  physical  phenomena  of  expansion  and  contraction 
in  the  vulcanization  process  are  by  some  considered  as  dis- 
advantages, but  these  can  be  so  well  controlled  by  modern 
methods  of  manipulation,  that  they  should  not  be  con- 
sidered. 

Red  and  pink  rubber  are  by  many  considered  injurious 
because  of  the  coloring  matter,  vermilion  (mercuric  sul- 
phide). This  criticism  is  unjust,  because  pure  mercuric 
sulphide  is  insoluble  in  water,  alcohol,  alkali,  and  all  acids 
(excefjt  nitrohydroehloric  acid),  which  under  no  condition 
should  ('oine  in  contact  with  red  or  pink  vulcanite,  as  this 


198 


RUBBER  AND  VULCANITE 


acid  converts  HgS  into  HgCl2  (corrosive  sublimate).  Only 
high  grades  of  rubber  should  be  used  in  the  mouth,  as  the 
cheap  grades  may  contain  injurious  impurities. 


INSTRUMENTS  AND  APPLIANCES   USED  IN  VULCANITE 

WORK 


Wax  Spatulas. — These  are  instruments  used  in  manipu- 
lating wax.    There  are  different  types  of  these  instruments, 


Fig.   104 


'  !!■    S    .  >  iS 


MO 


as  carvers,  ironers,  knives,  and  spoons.    Carvers  are  small 
knives  and  scrapers.      Nos.  1  and  2  of  the  Evans  set  are 


APPLIANCES   USED  IN   VULCANITE   WORK       199 

of  this  class  (Fig.  104).  (The  No.  3  of  this  set  is  a  bur- 
nisher for  tinfoil.)  Ironers  have  sufficient  bulk  of  metal 
in  their  ends  to  convey  heat  to  the  wax.    They  are  of  various 


Fig.   105 


forms  designed  to  facilitate  the  work.  Fig.  105  shows 
a  number  of  these  instruments.  Knives  are  larger  than 
the  knife-shaped  carver  and  are  designed  for  coarser 
work.     Spoons  are  for  melting  and  carrying  wax.     These 


200 


RUBBER  AND  VULCANITE 


various  classes  are  often  combined  in  double-end  instruments, 
especially  so  with  the  knife  and  spoon  (Fig.  106). 


Fig.  106 


Flasks. — There  are  a  great  many  varieties  of  vulcanite 
flasks  upon  the  market.  They  are  made  of  iron  or  brass. 
Iron  has  the  greater  affinity  for  oxygen  and  sulphur  in 
vulcanizing,  and  so  is  not  as  desirable  as  brass  for  this 
purpose.     The  brass  flasks  are  the  more  easilv  cleaned. 


APPLIANCES   USED  IN   VULCANITE  WORK       201 


Each  time  they  are  used,  they  should  be  thoroughly  cleaned 
with  a  stiff  brush  and  sapolio. 


Fig.   107 


202 


RUBBER  AND  VULCANITE 


The  Star  flask  is  one  of  the  oldest  forms,  and,  being  rever- 
sible, is  probably  adapted  to  more  cases  than  any  other 
(Fig.  107).  The  Wilson  flask  is  characterized  by  a  very 
narrow  rim  upon  the  lower  section,  with  a  correspondingly 
wide  rim  in  the  upper  section.  It  is  designed  to  be  used 
for  full  cases  only,  and  with  the  Donham  spring  clamp 
(Fig.  108).  The  Donham  flask  is  shown  in  the  Donham 
spring  clamp  (Fig.  109).  The  Whitney  flask  is  very  much 
used.    There  are  two  sizes,  the  larger  being  five-sixteenths 

Fig.  108 


of  an  inch  deeper  than  the  smaller.  Fig.  110  shows  the 
regular  size  with  springs  upon  the  bolts  to  aid  in  closing 
the  flask. 

The  box  flask  is  designed  for  interdental  splints  and  any 
extra  large  pieces  of  vulcanite.  It  is  made  in  two  sizes,  one 
as  large  as  can  be  used  in  a  two-flask  vulcanizer  and  the 
other  for  the  three-flask  vulcanizer  (Fig.  111). 

Flask  Presses.— The  flask  press  (Figs.  112,  11.3,  114)  is  an 
indispensable  appliance  in  a  well-equipped  laboratory,  and 
yet  probably  its  improper  use  has  caused  more  misfit  vul- 


APPLIANCES   USED  IN   VULCANITE  WORK       203 

Fig.   109  Fig.  110 


204 


RUBBER  AND  VULCANITE 


canite  dentures  than  all  other  causes.    When  the  principles 
involved  in  the  flask  press  and  its  use  are  understood,  there 


Fig.  112 


Fig.  113 


APPLIANCES   USED  IX  VULCANITE   WORK       205 

should  be  no  trouble  in  handling  it.  All  plasters  expand 
and  are  compressible,  some  excessively  so.  French's  regular 
dental  plaster  is  the  best  and  most  commonly  used  by  the 
profession,  so  these  statements  are  in  connection  with  this 

Fig.   114 


plaster.  A  molar  tooth  one-half  inch  in  diameter  under  a 
thousand  jjounds'  pressure  would  be  driven  into  well-set 
plaster  one-twentieth  of  an  inch.  Rubber  when  cold  is  very 
tenacious  and  will  resist  a  very  heavy  pressure  for  a  short 


206  RUBBER  AND  VULCANITE 

time,  but  will  gradually  yield.  Plaster  compresses  to  its 
full  extent  in  a  very  few  seconds.  It  is  easy  to  comprehend 
that  if  an  excess  of  rubber  is  placed  over  the  teeth  upon  one 
side,  and  heavy  pressure  is  applied,  that  the  teeth  will  be 
driven  into  the  plaster  encasement  and  consequently  the 
teeth  upon  that  side  of  the  denture  will  be  too  long.  It 
can  also  be  comprehended  that  if  the  cast  is  formed  of 
regular  plaster,  and  excessive  rubber  and  pressure  be  applied 
to  the  vault  of  the  cast,  that  it  will  be  pressed  upward  and 
the  plate  warped. 

We  shall  now  consider  the  power  of  the  press.  The  screw  is 
a  combination  of  the  lever  and  wedge,  and  its  power  is 
calculated  by  multiplying  the  circumference  described  by 
the  lever  by  the  pitch  of  the  screw\  The  Buffalo  Dental 
Manufacturing  Co.  No.  2  press  (Fig.  113)  has  a  handle 
8  inches  long,  hence  describes  \a  circumference  of  25  + 
inches.  There  are  ten  threads  to  the  inch,  hence  a  pitch 
of  yV  of  an  inch.  An  allowance  must  be  made  for  friction 
in  the  screw,  but  |-  will  be  very  liberal,  when  we  shall  have 
for  every  pound  of  force  applied  at  the  end  of  the  handle, 
two  hundred  pounds'  pressure  under  the  screw,  or  a  ton  for 
every  ten  pounds  of  force.  If  the  force  is  applied  at  the 
middle  of  the  handle  it  will  produce  one-half  as  much  pressure 
or  a  ton  for  every  twenty  pounds  of  force.  It  is  now  easily 
understood  why  plates  are  warped  and  these  heavy  malleable 
iron  presses  are  sometimes  broken. 

Vulcanizers. — There  are  in  use  at  the  present  time  many 
forms  of  vulcanizers.  It  is  unnecessary  to  enumerate  them. 
The  description  will,  therefore,  be  confined  to  one  of  the 
best  examples  of  the  somewhat  extensive  list. 

The  Lewis  Cross-bar  Vulcanizer  (Fig.  115)  embodies  many 
valuable  improvements,  and  is  probably  one  of  the  strongest, 
safest,  and  most  convenient  vulcanizers  of  the  cross-bar 
pattern  in  use. 

The  boiler  is  hand-made  from  copper,  rolled  expressly  for 
this  form  of  vulcanizer,  and  is  of  unusual  thickness.  The 
cap  is  ribbed  on  the  under  side  to  resist  any  strain  which 
may  be  put  upon  it.     This  cap  has  but  two  holes  drilled 


APPLIANCES   USED  IN   VULCANITE  WORK       207 

in  it:  one  for  the  mercury  bath,  to  which  the  thermometer 
is  attached;  the  other  for' the  "manifold,"  which  carries  the 
safety-^•al^•e,  bh^w-off,  gas  regulator,  or  steam  gauge  (Fig. 
116).'  The  ring  surrounding  the  boiler  is  of  cast  steel,  and 
is  therefore  of  ample  strength.  Besides  the  lugs  for  taking 
the  strain  off  the  cross-bar  and  bolt,  it  has  a  dovetailed 
projection  for  the  insertion  of  a  lifting  handle  (Fig.  117). 

Fig.   115 


It  will  be  observed  that  when  the  cross-bar  and  cap  are 
removed,  there  are  no  swinging  bolts  or  attachments  to  the 

The  cross-bar  is  of  an  improved  form,  and  is  made  oi 
cast  steel.  One  end  is  at  right  angles  to  the  main  bar,  and 
terminates  in  projections  which  catch  under  the  lugs  on  the 


208 


RUBBER  AND   VULCANITE 


ring.  Over  the  projections  is  a  small  rib  which  prevents  the 
bar  from  dropping  out  of  position.  The  other  end  of  the 
cross-bar  has  an  enlarged  portion  for  the  reception  of  the 
bolt,  and  is  terminated  by  a  handle. 


Fig.  116 


Fig.   117 


Fig.  118 


The  vulcanizer  is  closed  by  one  bolt  suspended  in  a  slot 
on  the  hand-end  of  the  cross-bar.  The  bolt  is  squared  to 
prevent  rotation,  and  is  surrounded  by  a  spring  for  the  pur- 
pose of  disengaging  it  from  the  lugs  when  the  nut  is  loosened, 
and  for  always  retaining  the  bolt  perpendicularly  and  forcing 
it  in  place  automatically. 

The  vulcanizer  is  opened  by  loosening  the  nut  on  the  bolt 
by  means  of  the  wrench  furnished  for  the  purpose  (Fig.  118). 
The  bolt  will  be  forced  downward  through  the  action  of  the 
spring.  The  handle  of  the  cross-bar  is  then  seized,  and  with 
the  thumb  against  the  nut  it  is  pressed  until  the  bottom  of 


THE   USE  OF  GAS  AND  TIME  REGULATORS      209 

the  bolt  is  disengaged  from  the  higs,  when  the  bar  mav  be 
lifted  (Fig.  119). 

Fig.   119 


INSTRUCTIONS  FOR  THE  USE  OF  GAS  AND  TIME 
REGULATORS 


"The  gas  regulator  {Fig.  120)  is  secured  to  the  cap  by 
means  of  the  short  iron  pipe  or  coil.  This  is  screwed  into  a 
hole  drilled  through  the  cap  of  the  vulcanizer,  and  tapped 
with  a  'one-eighth  gas-pipe  tap.'  If  the  vulcanizer  has  a 
'Lewis  manifold'  attached  to  the  cap  of  the  vulcanizer, 
remove  the  screw  between  the  blow-off  and  safety  valve 
and  screw  the  coil  pipe  in  its  place.  After  the  gas  regulator 
has  been  properly  fitted,  place  the  vulcanizer  in  the  jacket 
and  in  the  position  in  which  it  is  to  be  used.  Connections 
between  the  time  reguhitor,  gas  regulator,  and  gas  burner 
are  made  by  means  of  rubber  tubing.  The  engraving  (Fig. 
14 


210 


RUBBER  AND   VULCANITE 


121)  illustrates  the  correct  method  of  connecting  gas  and 
time  regulators  to  vulcanizers.  Cut  a  piece  of  tubing  of 
sufficient  length  to  reach  from  the  gas-supply  tap  to  the 
time  regulator,  and  connect  them;  cut  off  another  piece  to 
reach  from  the  time  regulator  to  the  gas  regulator,  and 
attach  to  the  gas  regulator  by  the  upright  or  straight  nipple 


Fig.  120 


on  top  of  the  No.  4  Lewis  gas  regulator;  then  connect  the 
downward  curved  tube  of  the  gas  regulator  to  the  gas  burner 
under  the  vulcanizer  with  another  piece  of  rubber  tubing. 

"The  time  regulator  is  more  convenient  when  placed  on 
a  bracket  near  the  gas-supply  pipe.  It  is  then  out  of  the 
wa}^,  and  not  likely  to  be  broken  from  contact  with  tools, 
and  can  also  be  used  as  a  timepiece. 


THE   USE  OF  GAS  AND   TIME  REGULATORS      211 

"To  Set  the  Time  Regulator. — When  the  valve  lever  on  top 
of  the  time  regulator  (Fig.  121)  is  engaged  with  the  screw 
upon  the  minute  arbor  on  the  back  of  the  clock,  the  valve 

Fig.   121 


is  held  open  for  a  length  of  time  depending  upon  whether 
the  lever  is  engaged  with  the  first,  second,  or  third  thread 
of  the  screw;  and  the  lever  will  be  cast  off,  and  the  valve 


212  RUBBER  AND   VULCANITE 

closed  when  the  minute  hand  reaches  the  figure  XII. 
When  the  minute  hand  is  at  IX  the  lever  will  be  cast  off 
at  the  end  of  fifteen  minutes,  if  it  is  engaged  with  the  first 
thread  of  the  screw  from  the  end;  an  hour  and  a  quarter,  if 
engaged  with  the  second  thread,  and  so  on.  A  trial  should  be 
made,  and  the  time  ascertained  which  is  necessary  for  heating 
the  vulcanizer  to  the  vulcanizing  point,  and  this  time  should 
be  added  to  the  proposed  time  for  vulcanizing.  We  have, 
therefore,  the  following: 

"Rule. — Turn  the  minute  hand  to  as  many  minutes 
before  the  hour  as  the  number  of  odd  minutes  desired;  then 
put  the  end  of  the  lever  in  the  threads  of  the  screw  upon 
the  minute  arbor  at  the  back  of  the  clock.  The  first  thread 
from  the  end  gives  the  odd  minutes  to  which  the  clock  is 
set;  the  next  and  each  succeeding  thread  gives  a  full  hour. 
For  example :  For  an  hour  and  twenty  minutes,  set  the  minute 
hand  at  the  figure  VIII,  and  engage  the  lever  in  the  second 
thread  from  the  end  of  the  screw.  At  the  end  of  that  time 
the  lever  will  disengage  and  automatically  shut  off  the  gas 
from  the  vulcanizer.  If  this  were  to  be  an  hour  longer — i.  e., 
two  hours  and  twenty  minutes — the  lever  should  be  placed 
on  the  third  thread  of  the  screw.  For  three  hours,  set  the 
minute  hand  at  XII  and  engage  the  lever  in  the  third  groove 
of  the  screw. 

Steam  Pressure. — "Those  who  use  vulcanizers  should  be 
thoroughly  informed  as  to  the  nature  and  properties  of 
steam.  The  fact  should  be  borne  in  mind  that  a  vulcanizer 
is  subject  to  the  same  laws  and  conditions  as  a  steam  boiler, 
which  it  is  in  fact,  and  although  it  is  comparatively  safe 
and  easily  operated,  it  may,  by  carelessness  or  ignorance  in 
its  management,  become  exceedingly  dangerous. 

"The  following  table  of  steam  pressure  will  be  found  con- 
venient for  reference,  as  it  has  been  corrected  so  that  it 
shows  the  true  temperature  for  any  pressure  indicated  by 
the  steam-gauge.  Fractions  are  omitted,  and  the  nearest 
whole  number  is  used  instead.  The  French  table  generally 
used  shows  14.7  pounds'  pressure  at  212°,  whereas  the 
steam-gauge  at  that  temperature  will  indicate  0,  unless  by 


THE   USE  OF  GAS  AND  TIME  REGULATORS      213 

the  expansion  of  heated  air  confined  in  the  vulcanizer.  The 
gauge  is  therefore  just  one  atmosphere  lower  than  the  French 
table : 


Table  of  the  Elastic   Force  of  Steam'  (Corrected  to  Corre- 
spond WITH  THE  Steam  Gauge) 

Degrees  of  temperature,  Elastic  force  in  pounds 

per  sqtiare  inch. 


Fahrenheit. 

212  . 

220  . 

230  . 

240  . 

250  . 

260  . 

270  . 

280  . 

290  . 

300  . 

310  . 

320  . 

330  . 

340  . 

350  . 

360  . 

370  . 

380  . 

390  . 

400  . 

410  . 

420  . 

430  . 

440  . 

450  . 

460  . 

470  . 

480  . 

490  . 

£00  . 

510  . 

520  . 

530  . 

540  . 

550  . 


0 

2 

6 

10 

15 

21 

27 

31 

43 

52 

63 

75 

89 

104 

120 

140 

160 

180 

205 

234 

264 

296 

335 

375 

415 

455 

515 

565 

603 

663 

721 

793 

864 

937 

1015 


"  It  will   be  noticed  that  as  the  temperature  rises  the 
pressure  of  steam  increases  in  constantly  increasing  ratio 

>  General  imitructionu  for  operating  dental  vulcaiiizern,   Iluffalo   Dr-ntal   Manufac- 
turing Co.,  July.  1898. 


214  RUBBER  AND  VULCANITE 

for  equal  increments  of  heat,  the  pressure  being  nearly 
doubled  by  the  addition  of  50°  to  the  temperature.  This 
fact  will  show  the  necessity  of  care  and  watchfulness  while 
vulcanizing. 

"The  bulb  of  the  thermometer  is  set  in  a  mercury  bath. 
This  is  the  small  cup,  forming  a  part  of  the  vulcanizer  cap, 
to  which  the  thermometer  case  is  screwed.  This  cup  should 
contain  sufficient  mercury  to  insure  its  touching  the  bulb 
of  the  tube  when  the  thermometer  case  is  screwed  down 
properly.  This  makes  a  metallic  connection  between  the  ther- 
mometer bulb  and  the  vulcanizer  cap,  and  is  absolutely  neces- 
sary for  the  proper  indication  of  heat  by  the  thermometer. 

"Should  the  mercury  column  separate,  it  can  usually  be 
reunited  by  removing  the  tube  from  the  thermometer  case, 
holding  it  perpendicularly,  and  striking  the  bulb  with  some 
force  upon  the  palm  of  the  hand,  or  by  holding  the  tube 
by  the  bulb  and  giving  it  a  sudden  flirt.  If  the  vulcanizer 
is  used  with  the  thermometer  in  this  condition,  it  should  be 
remembered  that  it  is  the  whole  column  that  denotes  the 
heat,  and  allowance  should  be  made  for  the  broken  part, 
^.  e.,  if  there  is  enough  mercury  separated  to  fill  the  space  of 
10°,  the  remainder  of  the  column  should  only  rise  to  10° 
less  than  the  temperature  desired. 

"Directions  for  inserting  a  new  tube  in  the  thermometer 
case  will  generally  be  found  on  the  package  containing  the 
tube  and  scale. 

"Thermometers  are  accurately  marked,  by  test  instru- 
ments, at  the  212°  and  320°  points,  and  the  scales  are 
especially  graduated  for  each  tube,  as  the  positions  of  the 
points  above  named  vary  in  different  tubes.  Each  tube 
must,  therefore,  be  used  with  its  own  scale,  and  in  fitting  it 
to  the  case,  care  should  be  taken  that  the  black  mark  on  the 
tube  indicating  the  320°  point  is  brought  exactly  opposite 
to  the  320°  point  on  the  scale. 

"The  thermometer  does  not  always  give  a  correct  indica- 
tion of  the  heat  of  the  vulcanizer.  It  only  gives  the  tem- 
perature of  the  vulcanizer  top,  which  may  not  be  that  of  the 
flask.    In  fact,  the  indications  of  the  thermometers  employed 


THE   USE  OF  GAS  AND  TIME  REGULATORS        215 


Fig.   122 


on  vulcanizers  are  almost  invariably  too  low,  owing  to 
imperfect  conduction  of  heat,  radiation,  etc.;  and  the  vul- 
canization temperature,  instead  of  being  320°,  as  indicated, 
is  more  usually  330°  to  340°." 

The  plan  of  providing  a  mercury  bath  for  the  reception 
of  the  bulb  is  a  great  improvement  over  the  old  way,  and 
prevents  the  fracture  of  the  bulb  by  the  great  pressure  of  the 
steam,  which  was  of  such  frequent  occurrence  when  the 
thermometer  was  in  direct  contact  with  the  latter. 

Damage  to  the  glass  bulb  of  the  thermometer  is  manifested 
by  a  rise  in  the  mercury,  which  cannot  be  brought  down  to 
the  usual  vulcanizing  point  by  turn- 
ing off  the  flame  of  the  burner;  con- 
sequently the  thermometer   ceases 
to  correctly  indicate  the  degree  of 
heat,   and   imperfect    vulcanization 
is  the    result.     Leakage    of    steam 
around  the  packing  of  the  vulcan- 
izer  should  also  be  guarded  against, 
as  in  such  cases  all  of   the  water 
may  escape  from  the  apparatus  be- 
fore   the    vulcanizing   is    complete. 
Loss  of  all  of  the  water  in  the  vul- 
canizer  may  be  detected  by  a  per- 
sistent fall  of    the  mercury,    even 
when  the  gas  flame  is  greatly   in- 
creased, and  when  this  phenomenon 
is  observed,  the  gas  should  be  turned 
off,  the  vulcanizer  allowed  to  cool, 
and  new  packing  adjusted.     Failure 
to  strictly  observe  this  rule  has  un- 
doubtedly resulted  in  many  serious 

accidents.  ■   •       i  i 

Vulcanizing.— The  flask  or  flasks  are  i)laccd  in  the  vul- 
canizer and  filled  about  three  quarters  with  clean  water. 
The  packing  should  bo  without  a  break  in  its  continuity, 
(Otherwise  the  steam  will  escape;  the  joint  between  the  pot 
and  cover  must  be  protected  from  adhesion  by  slightly  coat- 


fm.  123 


THE   USE  OF  GAS  AND  TIME  REGULATORS      217 

ing  it  with  black  lead  or  soapstone.  The  cover  is  then  put 
on,  but  the  valve  is  not  closed  until  the  heated  air  which  pre- 
cedes the  generation  of  steam  has  escaped ;  the  valve  is  then 
closed.  A  close  watch  must  be  kept  on  the  thermometer  or 
gauge  until  the  vulcanizing  point  is  reached,  unless  a  time 
regulator  is  used. 

Fig.  124 


Flask-tongs. — Fig.  122  shows  a  useful  form  of  flask-tongs 
for  lifting  flasks  from  the  vulcanizer.  "^'hey  are  made  of 
sufficient  length  to  reach  the  bottom  of  a  three-case  vulcan- 
izer,  and  will  securely  grip  the  flask. 

Files. — Fig.  12o  illustrates  some  excellent  forms. 


218 


RUBBER  AND   VULCANITE 


Vulcanite  Trimmers. — There  are  a  great  vaiiety  of  scrapers 
and  chisels  from  which  each  operator  may  select  such  as 
seem  best  adapted  to  his  hand.  The  writer's  preferences 
are  the  ones  here  illustrated  (Fig.  124). 


GRINDING  AND  POLISHING 

In  the  construction  of  artificial  dentures  upon  any  base, 
grinding  and  polishing  are  very  important  operations  and 
require  efficient  equipment  for  their  accomplishment.  For 
this  purpose  a  small  lathe  of  suitable  construction  is  neces- 
sary. These  lathes  will  require  approximately  one-sixth 
horse-power,  which  may  be  provided  by  either  electricity, 
water,  steam,  or  the  foot.     The  desirability  of  the  power 

Fig,   125 


chosen  is  in  the  order  named.  However,  steam  is  rarely 
used  in  a  dental  office  because  of  the  expense  of  installing 
and  maintenance.  There  are  many  patterns  of  these  imple- 
ments from  which  the  dentist  may  select.  There  are  two 
general  principles  involved  in  all  of  these  appliances:  (1) 
The  motor  and  lathe  are  combined  as  one  implement;  (2)  the 
motor  and  lathe  are  separate  and  coupled  together  with  a 
band  or  cord. 


GRINDING  AND  POLISHING 


219 


The  electric  current  is  most  convenient  and  serviceable 
when  it  can  be  had  in  the  office.  Fig.  125  represents  an 
apparatus  of  the  first  type,  that  is,  motor  and  lathe  com- 
bined. This  electric  lathe  is  admirably  adapted  to  general 
laboratory  uses  or  as  an  operating  room  lathe.  Its  bearings 
are  completely  protected  from  dust.     It  is  noiseless,  and  is 


constructed  with  such  precision  that  its  motion  is  hardly 
perceptible.  It  is  ada[>ted  to  the  110-volt  direct  current, 
and  has  sufficient  power  for  all  purposes  required  by  the 
dentist.  It  requires  no  sj)ecial  table,  hence  can  be  placed  in 
any  posititni  at  the  convenience  of  the  ()])erat()r.  It  has  a 
range  of  speed  varying  from  1000  to  4000  revolutions  per 
minute.     The  regulation   of  the  speed,   and   starting  and 


220 


RUBBER  AND  VULCANITE 


stopping  of  the  lathe  are  effected  by  the  milled  stud.  The 
chucks  are  held  upon  the  shaft  of  the  motor  by  friction,  and 
can  be  removed  while  the  motor  is  in  motion  or  stationary  by 
turning  the  milled  nuts  near  the  ends  of  the  shaft.  These 
motors  can  be  obtained  for  other  voltages  and  for  the  alter- 
nating current. 

Fig.  126  is  a  lathe  of  the  second  type,  and  can  be  operated 
by  any  power  through  a  cord.  This  illustration  shows  a 
convenient  arrangement  of  lathe  and  foot  power. 

These  lathes  are  all  provided  with  various  forms  of 
chucks  for  grinding  stones,  buffers,  and  polishing  brushes. 
Figs.  125  and  126  each  show  a  stone  mounted  chuck  upon 
one  end  of  the  shaft,  and  the  tapered  screw  cut  spindle  for 
buffers  and  polishing  brushes  at  the  other  end. 


Fig.   127 


Fig.  127  is  a  typical  set  of  chucks,  and  Fig.  128  a  lathe  head. 
Most  makers  of  lathes  furnish  an  extra  clutch  chuck  for  bur- 
ring engine  instruments.  Fig.  129  shows  such  a  chuck.  Fig. 
130  shows  an  additional  nut  the  author  has  had  added  to  the 
clutch  chuck  for  his  lathe.    By  this  means  a  three  by  one-half 


GRINDING  AND  POLISHING 


221 


inch  carborundum  stone  is  mounted.  The  figure  also  shows 
an  engine  mandrel  mounted  with  a  small  stone  in  the  clutch. 
The  author  has  no  use  for  any  other  stone  chuck,  and  no 
changes  are  required  except  in  the  small  stones,  burs,  and 


Fig.   129 


bits  used  in  the  chuck.  Fig.  1.31  is  the  "Ideal  Emery  Cloth 
Arbor,"  put  upon  the  market  by  Samuel  A.  Crocker  &  Co., 
Cincinnati.  This  is  an  especially  useful  addition  to  the 
lathe  for  vulcanite  work. 

The  lathe  should  be  kept  clean,  well  oiled,  and  true  running. 
Grinding  is  a   very  important  accomplishment — indeed,  it 


222 


RUBBER  AND  VULCANITE 


may  be  called  a  fine  art  in  mechanical  dentistry — and  can 
be  acquired  only  by  technical  training  and  the  use  of  true- 


FiG.   130 


Fig.   131 


Fig.   132 


running  and  well-cared-for  equipment.     Next  to  the  lathe 
running  true,  the  stone  must  be  kept  true  and  sharp;  this  is 


GRINDING  AND  POLISHING  223 

accomplished  by  the  use  of  a  machinist's  emery  stone  dresser 
(Fig.  132).  This  stool  is  used  over  a  firm  support,  with  a 
moderate  pressure,  upon  the  rapidly  revolving  stone.  It 
not  only  produces  a  true  surface,  but  a  very  sharp  cutting 
one.    The  tool  should  be  applied  often. 

Stones. — The  stones  used  in  the  dental  laboratory  are 
made  of  either  corundum  or  carborundum. 

Corundum  is  a  mineral  found  in  Ceylon,  and  in  Pennsyl- 
vania, Georgia,  ^Massachusetts,  and  North  Carolina.  It 
occurs  in  crystals  of  the  form  of  double  six-sided  pyramids 
of  various  sizes,  and  in  some  localities  in  large  masses  without 
crystalline  form.  Corundum  is  an  aluminum  oxide  having 
a  formula  AI2O3.  Emery,  the  use  of  which  preceded  corun- 
dum as  an  abrasive  agent  in  the  dental  laboratory,  is  a 
coarse  variety  of  corundum.  Corundum  is  prepared  for 
use  by  crushing  in  an  iron  mortar.  The  required  size  grit 
is  mixed  with  finely  ground  shellac  in  the  proportion  of 
3  ounces  of  corundum  to  1  of  shellac,  and  formed  in  iron 
molds  by  the  aid  of  heat  and  pressure.  The  surface  shellac 
is  dissolved  out  with  alcohol,  leaving  the  abrasive  crystals 
exposed.  Wheels  made  of  corundum  require  to  be  run  wet, 
otherwise  the  frictional  heat  will  draw  the  softened  shellac 
bond  to  the  surface,  producing  a  glaze  which  is  non-abrading. 

Carborundum  is  a  manufactured  grit;  it  is  harder  and 
more  brittle  than  corundum,  and  is  next  to  the  diamond  as 
an  abradent.  Carborundum  was  made  experimentally  in 
1893  by  Mr.  G.  E.  Acheson,  and  is  now  manufactured  on  an 
extensive  scale  at  Niagara  Falls.  It  is  made  of  a  mixture  of 
finely  divided  coke,  pure  silica  sand,  sawdust,  and  salt 
(NaCl).  Ten  tons  of  this  mixture  is  placed  in  a  furnace 
Hi  feet  long  by  (i  feet  wide  and  8  feet  high.  Electrodes  are 
connected  at  the  centre  of  each  end  with  a  core  of  crushed 
coke.  About  1  ()()()  horse-power  of  energy  is  utilized  at  an 
average  voltage  of  185,  reaching  a  temperature  approxi- 
mating I'AHf  F.  The  salt  acts  as  a  flux.  The  sawdust 
burns  out,  leaving  the  mass  i)or()Us  for  the  escape  of  gases. 
The  current  is  applied  for  thirty-six  hours;  it  is  then  with- 
drawn and  the  mass  given  time  to  cool.     About  two  tons 


224 


RUBBER  AND  VULCANITE 


of  crystals  are  formed  about  the  core,  consisting  of  the 
carbide  of  silicon  (CSi).  These  crystals  are  crushed,  washed, 
and  sieved,  mixed  with  feldspar  and  clay  as  a  bond,  molded 
into  shape  under  heavy  pressure,  and  burned  in  a  kiln 
for  several  days.  Wheels  made  of  carborundum  may  be 
run  either  wet  or  dry.  It  is  claimed  for  them  that  they  do 
not  clog;  however,  the  surface  becomes  so  filled  with  dust 
that  they  are  not  nearly  so  effective  as  when  tooled  as 
previously  described.  The  wheels  have  a  tendency  to  wear 
untrue,  probably  due  to  imperfections  in  the  mixing  with 
the  bond  and  burning  in  the  kiln.  Frequent  tooling  over- 
comes this  defect  and  keeps  them  true  and  sharp  until  they 
are  worn  out. 

Fig.   133 


No.  0 


Represents  No.  4  wheel. 


BufEers. — Bufiing  wheels  and  cones  are  used  on  the  thread- 
cut  spindle  in  finishing  the  denture;  they  carry  fine  abra- 
dents  and  remove  small  defects  and  scratches  from  the 
surface  of  the  work.    They  are  made  of  various  materials,  as 


GRINDING  AND  POLISHING 

Fig.  134 


225 


12  3  4 


Fio.   135 


15 


226 


RUBBER  AND   VULCANITE 


felt,  cotton,  duck,  leather,  soft  wood,  cork,  and  disks  of 
cloth  or  chamois  leather  stitched  together.  Felt  is  probably 
the  best  and  most  commonly  used  material  for  dental 
buffers.  The  wheels  are  made  in  various  sizes  and  shapes. 
A  wheel  two  or  two  and  one-half  inches  in  diameter  and  one- 
half  inch  thick  is  an  excellent  size.  Knife-edge  wheels  are 
very  useful  in  some  places,  but  they  must  be  properly  used 
or  they  will  quickly  cut  a  groove.  They  also  wear  away 
rapidly,  thus  destroying  the  knife-edge  effect.  They  require 
frequent  tooling  with  a  knife  or  chisel  to  keep  them  turned 
to  an  edge.  Figs.  133,  134,  and  135  show  a  square-edge 
wheel,  knife-edge  wheel,  and  cone  respectively. 


Brushes. — Brush  wheels,  both  stiff  and  soft,  are  used. 
These  wheels  are  made  in  various  forms.  Their  wooden 
centres,  which  are  straight  drilled,  should  be  reamed  to  a 
taper.  Fig.  136  shows  a  suitable  reamer.  They  are  used 
on  the  threaded  taper  spindle.  The  bristles  are  either 
straight,  converging,  or  diverging.  The  stiff  converging 
wheel  is  excellent  for  carrying  the  abradent  between  the 
teeth  where  the  felt  cannot  reach.    The  soft  bristle  brush 


Fig.  139 


^ 


'*^^^''' 


\ 


228  RUBBER  AND  VULCANITE 

is  used  to  carry  the  finest  abradent  and  produces  the  gloss. 
Figs.  137,  138,  and  139  show  three  forms  of  brushes  for  the 
lathe. 

Finishing  Powders  for  Vulcanite. — Pulverized  pumice  stone 
for  buffing  and  prepared  chalk  for  glossing  are  especially 
suited  to  vulcanite  work. 

Pumice  stone  is  volcanic  scoria  or  lava.  Chalk  is  calcium 
carbonate,  a  soft  variety  of  limestone;  it  is  prepared  by 
freeing  it  from  particles  of  coarser  grit. 

Use  of  Stones. — The  stones  are  used  to  grind  the  porcelain 
teeth,  sharpen  instruments,  etc.  It  is  safer  to  run  the  stone 
at  a  slow  speed.  There  is  danger  of  chipping  and  checking 
the  porcelain  by  the  pounding  of  an  untrue  stone  and 
heat  produced  by  a  clogged  one.  If  the  stone  is  true  and 
clean,  and  the  tooth  held  with  light  pressure,  it  will  be 
rapidly  cut  with  hardly  perceptible  frictional  heat,  con- 
sequently no  chipping  or  crazing  of  the  porcelain.  By  the 
same  care  a  steel  instrument  may  be  ground  without  drawing 
its  temper,  as  indicated  by  the  blue  color  and  spoiled  cutting 
edge.  A  higher  speed  may  be  used,  but  greater  care  is 
required. 

Buffing. — The  buffing  is  done  by  first  using  the  large 
felt  wheel  and  pulverized  pumice  stone.  The  work,  the 
felt,  and  the  pumice  must  be  kept  thoroughly  wet,  other- 
wise sufficient  frictional  heat  may  be  generated  to  roughen 
the  vulcanite  and  possibly  warp  the  denture.  It  should  be 
obvious  to  the  student  that  if  the  work  is  held  at  one  place 
against  the  felt  carrying  an  abradent  a  depression  will 
be  cut  into  its  surface.  Hence  the  work  while  being  held 
against  the  buffer  must  be  kept  in  constant  motion.  This 
motion  should  be  a  steady  systematic  procedure,  not  of  a 
jerky,  indecisive  type.  The  denture  should  be  finished 
with  true  symmetrical  convex  or  concave  surfaces  in  keeping 
with  the  conformation  of  the  part.  Facets  show  either 
inexperienced  or  careless  buffing.  The  buffer  may  be  run 
at  high  speed,  in  which  case  the  work  must  be  held  with 
moderate  pressure  only  against  the  buflfer.  Usually  it  is 
safer  to  use  a  moderate  speed  and  greater  pressure,  and  in 


HEAT  229 

some  places  it  is  wise  to  use  the  lowest  speed  and  light 
pressure.  The  buffer  does  not  cut  of  itself,  but  it  carries 
and  applies  the  abradent,  therefore  the  efficiency  of  the 
buffer  is  largely  due  to  the  manner  in  which  the  abradent  is 
applied.  The  abradent,  saturated  with  water  to  the  con- 
sistency of  soft  mud,  is  applied  to  the  surface  to  be  buffed; 
and  the  farther  edge  is  placed  against  the  well-moistened 
buffer.  The  buffer  engages  a  small  amount  of  the  abradent 
and  carries  it  over  the  surface  of  the  work.  As  the  buffer 
wheel  rises  from  the  surface  of  the  work,  it  throws  off  a 
portion  of  the  abradent,  but  a  small  portion  is  embedded 
in  the  surface  of  the  buffer  to  be  again  carried  over  the 
surface  of  the  work.  As  the  work  is  pushed  forward,  more 
abradent  is  engaged  and  made  to  serve  its  purpose.  The 
work  is  given  a  sideways  movement  as  well  as  a  forward 
one  until  all  of  the  abradent  is  removed  from  the  surface 
of  the  work.  More  abradent  is  applied  and  the  operation 
repeated  until  the  work  is  suitably  finished.  If  the  buffer 
is  applied  to  the  nearer  edge  of  the  abradent  and  the  work 
drawn  forward  the  buffer  will  push  away  the  abradent,  of 
which  only  that  portion  adhering  to  the  buffer  and  making 
the  complete  circuit  will  be  effective.  This  method  is  waste- 
ful of  abradent,  time,  and  energy. 

Glossing. — The  glossing  is  done  with  the  rapidly  revolving 
soft  brush  wheel  and  the  prepared  chalk.  The  chalk  well 
moistened  with  water  or  alcohol  is  applied  to  the  surface  of 
the  work  and  held  lightly  against  the  brush  wheel.  As  in 
buffing,  the  work  is  pushed  against  the  brush.  With  the 
beginning  of  glossing  the  brush  wheel  is  moistened,  but 
later  is  run  dry.  Alcohol  is  the  preferred  moistener  for  the 
glossing  powder  because  it  serves  to  attach  the  powder  to 
the  work  and  quickly  evaporates,  leaving  the  powder  in  a 
dry  condition,  best  for  glossing. 

HEAT 

In  vulcanite  work  heat  is  required  for  warming  wax,  rubber, 
flasks,  and  converting  the  rubber  into  vulcanite. 


230 


RUBBER  AND  VULCANITE 


Bunsen  Burner.— For  all  these  operations  the  blue  or 
Bunsen  flarae  only  is  suitable.  Fig.  140  shows  a  Bunsen 
burner  designed  for  the  laboratory  bench  and  connected 
to  the  gas  cock  with  rubber  tubing.     Fig.   141   shows  a 


Fig.  140 


Fig.   141 


jeweller's  triple  burner,  one  of  which  is  a  Bunsen.  This 
burner  is  especially  useful  because  it  can  be  attached  to  a 
jointed  bracket,  thus  doing  away  with  the  gas  saturated 
rubber  tubing.     One  of  the  other  burners  gives  a  light 


HEAT 


231 


Fig.   142 


flame,  and  the  third  burner  gives  a  flame  suitable  for  solder- 
ing. These  extra  burners  are  often  convenient.  The 
burner  in  the  upright  position  only  is  in  commission,  and 
when  any  one  of  the  burners  is  turned  straight  downward 
the  gas  is  cut  off  from  all  of  them. 

Construction. — It  consists  of  a  straight  tube  with  a  suitable 
size  hole  near  the  lower  end  for  the  admission  of  air  in  suffi- 
cient quantity  to  produce  instant  combustion 
of  the  carbon,  thus  giving  a  blue  smokeless 
flame. 

Nature  of  the  Bunsen  Flame. — ^Fig.  142  is 
an  illustration  of  the  Bunsen  tube  and  flame. 
A  flame  is  gaseous  matter  heated  to  a  state 
of  incandescence.  The  flame  has  a  three-cone 
structure:  ^1  shows  the  mixed  gas  and  air 
being  heated;  the  inner  edge  of  the  light  cone 
B  indicates  that  the  gaseous  mixture  has 
reached  the  state  of  incandescence  and  has 
become  a  flame;  the  outer  edge  of  the  light 
cone  B  indicates  where  the  greatest  heat  has 
been  attained  and  that  the  flame  from  this 
point  outward  is  cooling  until  the  outer  edge 
of  cone  C  is  reached.  At  this  point  the 
mixed  gases  have  become  chemical  compounds 
and  cooled  below  the  temperature  of  incan- 
descence, hence  the  flame  ceases  to  exist.  It 
is  evident  that  the  greatest  body  of  heat  is 
between  B  and  C,  consequently  this  is  the 
portion  of  the  flame  in  which  to  quickly  heat 
an  instrument. 

Fig.  143  is  a  gas  stove  of  many  Bunsen  jets,  and  is  suit- 
able when  a  much  greater  amount  of  heat  is  required  than 
can  be  produced  with  the  small  burner. 

Alcohol  and  Gasoline. — In  some  of  the  large  office  buildings 
in  cities,  and  in  many  of  the  small  towns,  gas  is  not  obtain- 
able as  a  source  of  heat;  then  recourse  must  be  had  to  either 
alcohol  or  gasoline.  Alcohol  is  suitable  as  a  substitute  for 
the  Bunsen  burner  for  working  wax  and  resinous  compounds; 


232 


RUBBER  AND  VULCANITE 


it  is  cleanly,  odor  not  offensive,  but  the  heat  is  slow.  Fig. 
144  shows  a  good  form  of  waxing  lamp.  Gasoline  is  more 
powerful  and  less  expensive,  but  the  odor  of  the  material  and 


Fig.  143 


Fig.  144 


Fig.  145 


CONSTRUCTION  OF  VULCANITE  DENTURES      233 

of  the  product  of  its  combustion  are  disagreeable.  Fig.  143 
is  an  excellent  Bunsen  burner.  Fig.  14(3  is  a  large  heater 
suitable  for  general  heating  purposes  in  the  laboratory. 

Fig.   146 


Petroleum. — Oil  seems  to  be  better  adapted  for  the  vulcan- 
izer  than  either  alcohol  or  gasoline.  The  lamp  for  using  oil 
needs  no  description,  for  a  suitable  oil  burner  may  be  had  for 
every  make  of  vulcanizer. 


TECHNIQUE  OF  CONSTRUCTION  FOR  COMPLETE 
VULCANITE  DENTURES 

Synopsis. — Diagnosis  and  prognosis;  impressions;  casts; 
base-plates;  occlusion  and  contour  models;  mounting  on  the 
New  Century  Antagonizor;  grinding  and  .setting  up  the 
teeth;  trying  in;  flasking;  j)acking;  vulcanizing;  and  finishing. 

Diagnosis  and  Prognosis.—  "^rhe  imaginary  patient  for  whom 
complete  artificial  dentures  are  to  be  constructed  is  a  lady, 
aged  forty  to  fifty  \ears,  of  the  blonde  type,  but  not  stout 
built  (sanguine  temperament,  nervous  temperament  modi- 


234  RUBBER  AND  VULCANITE 

fication),  and  good  health.  The  mouth  has  been  edentulous 
for  at  least  two  years;  the  gums  are  well  resorbed  and  oval 
in  form;  the  vault  is  medium  in  height  and  oval  in  form. 
There  is  a  moderate  amount  of  submucous  tissue  underlying 
the  mucous  membrane;  no  pronounced  hard  or  soft  places, 
and  the  fluids  of  the  mouth  abundant  but  not  ropy.  A 
normal  average  case.  The  prognosis  is  favorable,  provided 
the  personal  equation  does  not  present  unusual  difficulties. 

Impressions. — For  the  upper  impression,  see  Chapter  II; 
classification,  normal.  Points  to  give  attention:  Tray  with 
fianges  low  enough  not  to  be  displaced  by  any  muscular 
action;  palatal  border  wax  accurately  adjusted;  cuspid 
eminence  wax;  plaster  with  hastener  mixed  thin;  heel  of 
tray  adjusted  first;  lip  raised  while  adjusting  the  anterior 
portion  of  tray;  tray  supported  with  the  index  finger  in  the 
centre  of  the  vault;  lip  and  cheeks  drawn  downward  marking 
the  frense,  and  external  compression. 

For  lower  impression,  see  Chapter  II;  classification  high 
ridge,  broad.  Points  to  give  attention:  Flanges;  lingual 
wax  roll ;  plaster  with  hastener  mixed  thin ;  the  buccal  tissues 
drawn  from  under  the  buccal  flanges;  frense  marked;  external 
compression,  and  the  tray  held  in  place  by  pressure  of  the 
thumbs  in  the  bicuspid  region. 

Casts. — The  impressions  are  permitted  to  stand  for  a  few 
minutes,  then  varnished  with  thin  shellac,  and  when  dry 
(three  to  five  minutes)  with  thin  sandarac.  As  many  coats 
of  sandarac  should  be  applied  as  may  be  necessary  to  secure 
a  glossy  surface,  permitting  each  coat  to  dry  before  applying 
the  next  one.  The  impressions  are  filled  with  Speace  com- 
pound of  the  consistency  of  stiff  putty,  or  a  slow,  hard  setting 
plaster  may  be  used;  either  must  be  thoroughly  jarred  into 
place.    (See  Chapter  III.) 

Base-plates.- — Heavy  tinfoil  (No.  20  to  60)  is  placed  upon 
the  cast,  over  which  a  sheet  of  paraffin  base-plate  wax  is 
adjusted  (any  of  the  resinous  base-plate  stock  material 
may  be  substituted  for  the  paraffin).  Soft  wax  is  built 
upon  the  base-plates  to  form  the  occlusion  and  contour 
models  as  described  in  Chapter  IV. 


CONSTRUCTION  OF  VULCANITE  DENTURES      235 

Occlusion  and  Contour  Models. — The  models  formed  on  the 
casts  are  tried  in  the  month,  removed  and  added  to  or  cut 
away  as  may  be  necessary  to  give  the  proper  restoration  of 
the  lower  third  of  the  face  at  rest.  The  models  should  be 
tested  with  a  spatula,  to  see  that  they  rest  with  uniform  press- 
ure upon  all  portions  of  the  alveolar  processes.  The  patient 
is  exercised  in  the  forward  and  backward  movements  of  the 
mandible.  These  movements  being  made  at  command,  the 
mandible  is  placed  in  the  retruded  position  and  the  occlusion 
guide  lines,  the  high  and  low  lip  lines,  and  the  median  line 
recorded  in  the  wax.  The  lower  model  is  removed  from  the 
mouth  and  the  bite  gauges  adjusted.  The  model  is  then 
replaced  and  the  mouth  closed  in  the  protruded  position, 
recording  the  inclination  of  the  condyle  path.  The  bite 
gauges  are  removed  from  the  low^er  models  and  the  fork  of 
the  face  bow  attached  to  the  upper  model.  The  face  bow 
is  adjusted  and  the  relationship  of  the  wax  model  to  the 
condyle  secured.     (See  Chapter  IV.) 

The  student  could  justly  conclude  that  all  of  the  preceding 
work  is  done  at  one  appointment  with  the  patient.  However, 
it  is  not  necessary  to  detain  the  patient  after  the  impressions 
are  secured;  a  second  appointment  may  be  made  for  the 
next  step.  During  the  absence  of  the  patient  the  impressions 
are  glossed,  filled,  and  permitted  to  harden  for  an  hour  or 
two.  The  impression  is  then  removed  from  the  cast  (see 
Chapter  III),  the  base-plate  formed,  and  the  ])reliminary 
work  done  upon  the  wax  model.  At  the  second  appoint- 
ment the  wax  models  are  adjusted  to  the  mouth  and  the 
required  data  of  marks  and  measures  secured.  The  color 
of  the  teeth  is  selected.  The  detail  of  determining  the  color 
cannot  be  discussed;  suffice  to  say  that  this  phase  of  the 
science  will  be  discussed  in  the  chapters  on  Porcelain  Teeth 
and  Esthetics;  also  that  the  color  for  the  type  of  the  imaginary 
patient  must  be  straw  yellow  modified  with  gray,  probably 
shade  39  or  41  of  the  S.  S.  W.  shade  bar;  possibly  as  much 
toning  with  gray  will  be  required  as  represented  in  shade  40. 
The  patient  is  again  dismissed  with  an  api)ointinent  for 
another  sitting.    During  the  absence  of  the  patient  the  casts 


236  RUBBER  AND  VULCANITE 

and  wax  models  are  mounted  upon  an  antagonizor,  the  teeth 
selected,  ground,  and  set  up.  At  the  third  appointment  the 
teeth  mounted  on  wax  are  tried  in  the  mouth.  The  details 
of  this  sitting  are  discussed  in  the  chapter  on  Esthetics. 
At  the  fourth  appointment  the  finished  dentures  are  placed 
in  the  mouth  and  thoroughly  inspected  before  dismissing 
the  patient. 

Mounting  on  Antagonizor. — The  face  bow  with  the  wax 
models  and  casts  are  assembled  and  mounted  on  the  New 
Century  antagonizor,  as  described  in  Chapter  V.  The  face 
bow  removed,  the  bite  gauges  are  used  to  secure  the  inclina- 
tion of  the  condyle  path,  as  described  in  Chapter  V. 

Grinding  and  Setting  Up. — A  section  of  the  wax  of  the  upper 
model,  represented  by  the  median  and  high  lip  lines,  is  removed 
with  a  warmed  wax  knife  (Fig.  106).  The  esthetics  involved 
in  selecting  the  artificial  teeth  cannot  now  be  discussed; 
however,  a  rule  may  be  given  for  determining  the  size  of 
the  teeth.  Length:  The  length  of  the  teeth  selected  should 
be  sufficient  to  fill  the  space  between  the  high  lip  line  and 
the  occlusal  plane.  JVidth:  The  crest  of  the  cuspid  teeth 
beginning  with  its  cusp  should  be  continuous  with  the  crest 
of  the  cuspid  eminence  developed  in  the  contoured  wax 
model  (see  Chapter  I,  also  Fig.  2);  therefore,  the  combined 
width  of  the  central,  lateral,  and  the  mesial  plane  of  the 
cuspid  is  the  length  of  the  space  from  the  median  line  to  the 
crest  of  the  cuspid  eminence.  The  distal  plane  of  the  cuspid 
and  the  bicuspids  and  molars  should  fill  the  space  between 
the  crest  of  the  cuspid  eminence  and  the  maxillary  tuber- 
osity. This  rule  for  length  and  width  is  only  applicable  to 
normal  or  nearly  normal  cases.  Extreme  and  abnormal 
cases  cannot  be  classified,  and  artificial  teeth  must  be 
selected  according  to  the  judgment  of  the  prosthetist. 

Grinding. — There  are  two  stages  of  grinding  a  set  of 
artificial  teeth.  The  first  stage  is  grinding  for  occlusion 
at  the  time  of  setting  up  the  teeth.  The  object  is  to  gain 
as  large  a  contact  surface  as  may  be  expedient,  and  to  so 
face  the  surfaces  as  to  crush  the  food  without  dislodging 
the  dentures.     The  second  stage  is  at  the  time  of  final 


CONSTRUCTION  OF  VULCANITE  DENTURES      237 

finishing  of  the  dentures,  and  is  designed  to  produce  edges 
for  catching  and  cutting  the  food;  also  to  remove  such 
points  as  may  interfere  with  antagonization.  The  first 
stage  of  grinding  may  be  done  before  any  of  the  teeth  are 
set  up,  or  each  tooth  may  be  ground  just  before  setting  up. 
The  first  method  is  more  expeditious  for  an  experienced 
workman,  but  the  second  method  is  more  comprehensible 
for  the  student  and  is  the  one  here  described. 

Setting  Up. — As  the  patient  is  in  middle  life,  the  anterior 
teeth  must  be  ground  to  represent  slight  wear.  This  is  done 
by  slightly  grinding  the  incisal  edge  of  the  incisors  so  as  to 
give  a  moderately  sharp  straight  edge,  removing  the  rounded 


edge  of  youth.  The  central  incisor  is  set  in  place  and  secured 
with  melted  wax  (P^ig.  147).  Setting  up  the  teeth  may  be 
facilitated  by  placing  a  small  roll  of  softened  yellow  wax 
upon  the  wax  model  into  which  the  cervical  end  of  the  teeth 
are  pressed  and  thus  held  while  the  lingual  portion  is  being 
filled  with  melted  wax.  This  lingual  wax  may  be  added  by 
dropping  on  from  a  pencil  or  stick  of  wax,  the  end  of  which 
is  melted  in  the  Bunsen  flame,  or,  the  melted  wax  may  be 
carried  to  place  in  a  wax  spoon  (Fig.  10()).  The  lateral 
incisor,  with  its  incisal  edge  straightened,  is  set  next  to  the 
central.  The  cuspid  with  its  mesial  incisal  edge  ground, 
thus  placing  the  apex  of  the  cusp  more  distally,  is  secured 


238 


RUBBER  AND  VULCANITE 


Fig.   148 


in  place.  These  three  teeth  fill  the  space  from  the  high  lip 
line  to  the  occlusal  plane,  and  from  the  median  line  to  and 
including  the  cuspid  eminence.  Their  labial  surfaces  describe 
the  segment  of  an  arc,  the  radius  of  which  is  the  straight 
line  from  the  mesioincisal  angle  of  the  cen- 
tral incisor  to  the  distoincisal  angle  of  the 
cuspid.  The  buccal  surface  of  the  bicuspids 
and  molars  form  a  straight  line,  but  one 
which  diverges  from  the  median  plane  of  the 
mouth.  The  bicuspids  and  molars  are  all 
ground  so  as  to  present  three  surfaces  to  its 
antagonist.  This  is  best  understood  by 
studying  Figs.  148  and  149.  The  bicuspids 
must  have  the  three  planes  upon  both  the 
mesial  and  distal  occlusal  surfaces,  while  the 
molars  have  but  the  three  straight  planes.  The  first  and  sec- 
ond bicuspids  and  first  molar  (see  Fig.  147)  are  set  in  order 
with  their  buccal  surface  forming  the  straight  divergmg  line. 
If  the  segment  of  the  circle  described  by  the  three  anterior 
teeth  is  continued,  it  will  pass  through  the  buccal  cusp  of  the 


Fig.  149 


first  bicuspid  and  diagonally  through  the  sulcus  of  the  second 
bicuspid  (Fig.  9).  The  second  upper  molar  is  not  set  until 
the  lower  teeth  are  mounted.  The  wax  about  the  six  mounted 
teeth  (Fig.  147)  is  smoothed  and  cooled  so  as  to  securely 
hold  them. 


CONSTRUCTION  OF   VULCANITE   DENTURES       239 

The  segment  of  Avax  between  the  meflian  and  higli  hp 
Hnes  upon  the  other  side  of  the  wax  model  is  removed  witli 
a  warmed  wax  knife.  The  six  teeth  for  that  side  are  then 
ground,  set  up,  and  waxed  securely. 

The  method  for  grinding  and  setting  up  the  lower  teeth 
is  similar  to  the  upper;  however,  there  are  some  important 
modifications.  The  section  of  wax  defined  by  the  median 
and  low  lip  line  upon  either  side  is  removed  and  a  small  roll 
of  wax  added  into  which  the  cervical  end  of  the  teeth  are 
inserted.  The  grinding  of  the  lower  teeth  differs  from  that 
of  the  upper  in  this:  The  facet  formed  on  the  incisal  edge  of 
the  upper  looks  lingually,  while  that  formed  upon  the  lower 
incisors  looks  labially.  The  mesial  edge  of  the  upper  cuspid 
is  extended,  while  in  the  lower  cuspid  the  mesial  edge  is 
shortened.  The  mesiodistal  groove  formed  in  the  upper 
bicuspids  and  molars  is  on  the  buccal  side  of  the  centre  of 
the  tooth,  while  it  is  placed  lingually  on  the  lower  (Fig.  149). 

There  are  two  methods  for  setting  up  the  lower  teeth. 
One  method  begins  by  setting  first  the  second  bicuspid  so 
that  it  shall  accurately  intercuspate  with  the  upper  first  and 
second  bicuspids.  This  is  followed  in  order  by  the  first 
bicuspid,  cuspid,  lateral,  central,  and  then  the  first  molar. 
The  other  method  begins  with  the  central  incisor  and  con- 
tinues in  order  backward.  The  reason  for  beginning  with  the 
anterior  is  to  assure  the  desired  expression,  and  that  the  lower 
teeth  shall  be  clear  of  the  upper  ones  by  nearly  one-sixteenth 
of  an  inch.  The  upper  anterior  teeth  should  overlap  the 
lower,  but  for  mechanical  reasons  they  caimot  overlap  one- 
thirfl  the  length  of  the  crown,  as  in  typical  natural  te(th. 
The  amount  of  the  overbite  will  be  governed  by  the  angle 
of  the  condyle  path  and  will  be  adjusted  at  a  later  stage  of 
the  operation.  The  difficulty  encountered  by  this  method  is 
to  get  the  bicuspids  to  interlock.  This  often  requires  that 
the  anterior  teeth  oxerlap  each  other  laterally,  especially  the 
cuspid  overlapping  the  lateral.  To  properly  overlap  any 
of  the  anterior  teeth,  either  lower  or  up})er,  the  mesiolingual 
angle  of  the  overlapping  tooth  should  b(;  ground  away  for 
nearly   its  entire   length.     Also  to   interlock  the   bicuspids 


240 


RUBBER  AND   VULCANITE 


it  may  be  necessary  to  soften  the  wax  about  the  upper 
bicuspids  and  molar  and  move  them  backward.  However 
it  may  he  accomplished,  the  bicuspids  must  interlock  or  inter- 
cuspate.  These  six  lower  teeth  being  secured  with  wax, 
the  segment  of  wax  on  the  other  side  of  the  median  line  is 
removed  and  the  six  teeth  mounted  on  that  side.  Fig.  150 
shows  the  twelve  upper  and  the  twelve  lower  teeth  mounted 
to  a  straight  horizontal  plane.  Should  any  of  the  teeth 
be  loose  in  their  setting,  they  are  made  fast  by  remelting  the 
wax  about  them  with  an  ironing  spatula  (Fig.  105),  and  the 
wax  about  all  of  the  teeth  thoroughly  chilled  for  the  next 
step  of  setting  the  lower  second  .molar. 


Fig.  150 


A  portion  of  the  hardened  wax  just  back  of  the  lower  first 
molar  is  removed  and  a  ball  of  softened  wax  set  in  its  place. 
The  occlusal  surface  of  the  second  molar  is  ground  into  the 
same  form  as  that  of  the  first  molar,  and  set  upon  the  softened 
ball  of  wax.  The  plane  of  the  occlusal  surface  of  the  second 
molar  should  be  nearly  parallel  with  the  plane  of  the  condyle 
path,  and  the  tooth  should  be  so  placed  that  the  disto- 
occlusal  margin  of  the  upper  first  molar  will  glide  upon  the 
buccosulcus  plane  of  the  lower  second  molar  when  the  teeth 
are  placed  in  lateral  occlusion.     Fig.  151  shows  the  teeth 


CONSTRUCTION  OF   VULCANITE  DENTURES      241 

in  lateral  occlusion  and  the  distoocclusal  margin  of  the  upper 
first  molar  in  contact  with  the  lower  second  molar.  It  is 
obvious  that  if  all  the  teeth  but  the  lower  second  molar 
are  set  in  hardened  wax,  and  it  in  softened  wax,  working 
the  condyle  joint  forward  and  backward  repeatedly  will  aid 
in  properly  adjusting  the  second  molar.  Correctly  placing 
the  three  molars,  the  upper  first  and  the  lower  first  and 
second,  is  the  key  to  the  mechanico-anatomical  antagoniza- 
tion;  and  the  secret  for  success  in  the  adjustment  of  these 
molars  is  in  keeping  the  disto-occlusal  margins  of  the  first 
molars  down.     They  may  be  depressed  a  trifle  below  the 

Fig.   151 


plane,  but  never  elevated  above  the  plane.  Herein  is  the 
distinction  between  the  mechanico-anatomical  arrangement 
of  artificial  teeth  and  the  variously  advocated  "anatomical" 
arrangement  of  them.  By  observing  Figs.  1,  2,  3,  and  4,  it 
will  be  seen  that  the  anatomical  arrangement  of  natural 
upper  teeth  is  that  the  occlusal  surfaces  of  all  the  teeth,  from 
the  central  incisors  to  and  including  the  distobuccal  cusp 
of  the  first  molars,  are  in  a  straight  horizontal  plane,  and 
that  the  second  and  third  molars  are  not  tilted,  but  stepped 
upward.  So  far  as  the  author  knows,  no  advocate  of  the  so- 
called  "anatomical  articulation"  has  ever  suggested  repro- 
16 


242  RUBBER  AND   VULCANITE 

ducing  this  upward  stepping  of  the  second  and  third  molars. 
Hence  there  never  has  been  a  system  of  anatomical  arrange- 
ment for  artificial  teeth,  for  they  have  all  been  adaptations, 
and  all  to  a  greater  or  less  extent  have  opposed  a  physical 
law.  The  physical  law  is  that  "force  moves  at  right 
angles  to  the  surface  from  which  it  emanates."  Therefore, 
it  is  evident  that  the  system  that  least  opposes  this  physical 
law  is  superior  in  at  least  this  one  respect.  It  is  evident 
that  if  the  molars  are  tilted  upward  at  any  angle  (the  greater 
the  angle  the  greater  the  leverage),  the  closing  movement 
of  the  mandible  must  force  the  upper  denture  forward,  and 
that  if  it  were  not  for  the  interlocking  of  the  bicuspids  the 
denture  could  not  be  retained  in  its  place.  As  the  first 
molars  must  assume  the  burden  of  crushing  hard  food,  it 
is  logical  to  reason  that  their  occlusal  surfaces  should  be 
parallel  to  their  alveolar  base  of  support.  If  the  crushing 
of  food  were  the  only  function  of  artificial  dentures,  then 
the  second  molars  should  be  placed  in  the  straight  occlusal 
plane;  however,  it  is  important  to  grind  the  food,  and  to 
have  the  dentures  so  constructed  that  they  are  balanced  in 
any  position  in  w^hich  they  may  be  occluded.  To  obtain  this 
balanced  relationship  of  artificial  dentures  it  is  necessary 
to  ha\'e  more  or  less  of  the  teeth  placed  in  harmony  with 
the  condyle  path;  but  to  secure  the  greatest  effectiveness 
in  crushing  and  grinding  the  food,  it  is  necessary  to  have  as 
few  teeth  out  of  the  horizontal  occlusal  plane  as  possible, 
hence  the  short  balancing  curve,  or  "compensating  curve." 
This  term  "short  balancing  or  compensating  curve"  is  in 
contradistinction  to  the  long  "compensating  curve,"  as  first, 
taught  by  Dr.  Bonwill. 

Having  developed  the  philosophy  of  this  peculiar  arrange- 
ment of  these  three  molars,  a  return  may  be  made  to  the 
technique. 

In  like  manner  the  three  molars  are  adjusted  on  the  other 
side  of  the  case. 

Proving  the  Antagonization. — A  critical  study  should  now 
be  made  of  the  antagonization  of  the  teeth  as  mounted. 
For  this  purpose  the  antagonizor  is  grasped  so  that  the 


CONSTRUCTION  OF   VULCANITE  DENTURES      243 

thumbs  and  fingers  may  manipulate  the  condyle  paths,  and 
the  three  movements  (incisal,  right  and  left  lateral)  are 
repeatedly  produced.  This  will  disclose  any  imperfections 
in  the  alignment  of  the  teeth.  Should  any  of  the  teeth 
prove  to  be  too  long  and  interfere  in  the  varied  movements, 
they  may  be  intruded  or  ground  upon  the  lathe.  The  teeth 
may  be  ground  while  mounted  in  wax,  provided  light  pressure 

Fig.   152 


is  u.sed  in  holding  them  against  the  stone,  and  the  stone  is 
sharp  and  true  runnimi.  The  requirements  of  well-antag- 
oni/x'd  teeth  are  that  there  shall  be  sufficient  points  of  con- 
tact in  any  position  in  which  they  may  be  closed,  in  ordinary 
use,  to  balance  them,  or  to  prevent  tlieir  displacement.  If 
the  teeth  are  placed  in  incisal  occlusion,  as  shown  in  Fig. 
152,  the  upper  and  lower  incisors  will  be  in  contact,  also 
the   upper    first    molars   (disto-occlusal   margin)  will   be  in 


244 


RUBBER  AND  VULCANITE 


contact  with  the  lower  second  molars.  It  will  be  only 
incidental  and  owing  to  an  irregularity  of  alignment  should 
there  be  any  points  of  contact  between  the  incisors  and 
molars,  for  the  upper  teeth  describe  a  straight  line  and  the 
lower,  by  inclining  the  second  molar,  describe  a  concave 
line;  and  a  concave  line  can  be  in  contact  with  a  straight 
line  only  at  its  extremities.  The  teeth  being  in  right  lateral 
occlusion,  that  is,  the  lower  carried  to  the  right  (Fig.  153), 
there  will  be  many  points  of  contact  on  the  right  side  but 


Fig.   153 


no  contact  on  the  left  side,  except,  because  of  the  pivotal 
movement,  the  lower  second  molar  is  carried  forward  and 
is  in  contact  with  the  disto-occlusal  margin  of  the  upper 
first  molar.  This  gives  the  so-called  three-point  contact,  as 
represented  by  the  molars  upon  the  left  and  the  cuspids  and 
molars  on  the  right  side.  The  teeth  being  placed  in  the  left 
lateral  occlusion  (Fig.  154),  the  same  relations  are  established 
for  that  side. 

In  this  critical  study  of  the  antagonization  of  the  teeth 
it  should  be  apparent  that  there  is  a  relationship  between 


CONSTRUCTION  OF  VULCANITE  DENTURES      245 

the  lateral  inclination  of  the  bicuspids  and  molars  and  the 
angle  of  the  condyle  path.  The  difference  in  width  of  the 
maxillte  and  the  mandible,  in  the  bicuspid  and  molar  region, 
necessitates  that  these  teeth  are  more  or  less  laterally 
inclined;  and  that  the  plane  described  by  the  lateral  move- 
ment varies  from  straight  to  sharply  concave,  with  the 
concavity  upward.  If  the  condyle  path  is  horizontal,  the 
lateral  movement  plane  will  be  straight;  but  if  the  condyle 
path  is  nearly  perpendicular,  the  lateral  movement  plane 
will  be  sharply  concave.    This  is  demonstrated  by  two  blocks 

Fio.  ]o4 


of  plaster  mounted  in  the  antagonizor,  and  the  lateral  move- 
ments made  until  the  blocks  are  so  ground  that  they  will 
be  uniformly  in  contact  at  every  point,  while  in  the  lateral 
movement.  If  the  teeth  have  not  been  correctly  inclined 
while  mounting,  they  may  be  corrected  by  softening  the  wax 
about  the  cervical  ends  of  the  teeth  with  a  hot  ironing  wax 
spatula  and  moving  the  cervical  ends  either  inward  or 
outward  as  required.  It  may  be  necessary  to  remove 
certain  of  the  teeth  and  detpen  the  sulci  and  possibly  shorten 
some  of  the  cusps.    When  the  teeth  are  ground  and  mounted 


246  RUBBER  AND  VULCANITE 

so  that  they  may  be  moved  in  any  direction  (three),  and  not 
meet  with  interfering  points,  also  have  the  largest  amount  of 
contact  surface,  the  critical  study  and  correction  may  be 
considered  as  completed.  Time  used  in  this  critical  work  is 
well  spent. 

To  complete  the  mounting  of  the  teeth  sufficient  wax  is 
cut  away  to  permit  the  upper  second  molars  being  set  in 
occlusion  with  the  lower  second  molars,  which  are  fixed 
in  position  with  melted  wax. 

It  is  noticeable  in  some  of  the  illustrations  that  there  is  a 
space  betw^een  the  lower  first  and  second  molars.  The  reason 
for  this  is  that  by  carrying  the  second  molar  forward,  surface 
contact  cannot  be  gained,  only  a  V-shaped  space  formed, 
while  by  carrying  it  backward  it  affords  a  longer  gliding 
surface  for  the  upper  first  molar  and  a  larger  contact  sur- 
face for  the  upper  second  molar. 


FINISHING  THE  MODEL  DENTURES 

The  teeth  being  now  accurately  mounted  and  antagonized, 
care  must  be  exercised  not  to  disturb  them  in  any  further 
manipulation.  As  the  outlines  of  the  wax  model  bases  are 
the  outlines  of  the  finished  dentures,  attention  should  be 
given  to  the  contour  of  the  wax  model  bases.  These  are 
completed  by  adding  wax  where  there  may  be  a  deficiency, 
cutting  away  excessive  wax  and  glossing  the  surface.  The 
Haskell  and  Gritman  spatulas  (4  and  5  respectively  of  Fig. 
105)  are  excellent  as  ironing  instruments,  and  the  Nos.  1 
and  2  instruments  of  the  Evans  carvers  are  especially 
suitable  for  carving.  There  are  two  methods  for  glossing — 
(1)  heat,  and  (2)  a  solvent.  The  heat  may  be  applied  to 
glossing  the  surface  either  by  passing  the  wax  model  base 
through  the  Bunsen  flame  with  a  moderately  rapid  motion; 
or  the  flame  may  be  pufi^ed  upon  the  surface  of  the  wax 
with  a  small  mouth  blowpipe.  An  expert  may  produce 
beautiful  results  with  the  flame,  but  the  novice  is  liable 
to  come  to  grief.     The  solvent  method  consists  of  wiping 


FINISHING  THE  MODEL  DENTURES  247 

the  surface  over  with  a  soft  cloth  (quarter  of  an  aseptic 
napkin)  moistened  with  a  wax  solvent.  The  most  convenient 
and  least  objectionable  solvent  is  chloroform.  The  teeth 
are  cleansed  of  wax  at  the  same  time  that  the  surface  is 
smoothed.  As  the  surface  is  covered  with  partially  dis- 
solved wax,  the  case  should  be  permitted  to  stand  until 
the  chloroform  has  evaporated.  The  evaporation  may  be 
hastened  by  using  a  blast  of  air. 

Proving  in  the  Mouth. — The  artificial  dentures  are  now 
ready  for  the  third  appointment  with  the  patient.  There 
are  two  phases  of  constructing  artificial  dentures  to  be 
given  consideration  at  this  sitting  of  the  patient — (1)  proving 
the  occlusion  and  antagonization,  and  (2)  developing  the 
esthetics. 

Proving  the  occlusion  and  antagonization  is  accomplished 
by  placing  the  well-cooled  model  dentures  in  the  mouth  and 
requesting  the  patient  to  close  the  "back  teeth,"  but  force 
should  not  be  used  upon  them,  as  they  are  only  in  wax.  If 
they  close  in  the  retruded  position,  as  constructed  upon  the 
antagonizer,  the  inference  is  that  the  occlusion  is  correct. 
However,  it  is  well  to  make  other  tests,  as  there  is  nothing 
about  prosthetic  dentistry  quite  so  uncertain  as  how  an 
edentulous  patient  may  close  the  mouth.  They  are  more 
liable  to  close  it  in  a  protruded  position  than  in  the  normal 
retruded  one.  As  a  further  test,  the  head  is  tilted  backward, 
the  prosthetist  parts  the  lips  slightly,  and  watches  the  result 
while  the  patient  performs  the  act  of  deglutition.  This 
act  will  necessitate  the  mandible  being  in  its  normal  retruded 
position.  Should  the  mandible  drop  })ackward  an  eighth  or 
a  quarter  of  an  inch,  the  student  may  feel  momentarily 
disheartened,  for  it  will  be  necessary  to  go  back  and  do  the 
work  all  over  again,  beginning  with  the  paraffin  base-plates 
and  occlusion  and  contour  models.  However,  the  student 
will  i^rofit  by  such  an  exi)ericnce  and  henceforth  give  more 
attention  to  his  occlusion  and  contour  models.  Should  the 
.  deglutition  test  prove  the  occlusion  in  retrusion  to  be 
correct,  the  test  for  equalized  pressure  is  applied.  Before 
making  this  test  it  is  better,  as  the  wax  has  been  absorbing 


248  RUBBER  AND   VULCANITE 

considerable  heat,  to  remove  the  model  dentures  from  the 
mouth  and  again  coil  them.  They  are  replaced  in  the 
mouth  and  just  firmly  held  in  retruded  occlusion.  An 
attempt  is  made  to  insert  a  thin-bladed  spatula  between 
the  bicuspids  and  molars  upon  first  one  side  and  then  the 
other.  Should  the  pressure  be  even  upon  the  two  sides, 
well  and  good;  but  should  there  be  a  separation  on  one  side, 
admitting  the  blade  of  the  spatula,  the  blade  should  be 
rotated  to  determine  the  extent  of  the  imperfection.  If  the 
imperfection  is  but  slight,  it  may  be  corrected  by  removing 
the  model  dentures  from  the  mouth,  placing  one  in  water 
to  cool,  drying  the  wax  of  the  other  (with  absorbent  cloth) 
about  the  non-contact  teeth,  softening  the  wax,  extruding 
the  teeth,  and  adding  melted  wax  as  indicated.  The  model 
dentures  are  returned  to  the  mouth  and  closure  made  until 
equal  pressure  is  obtained  upon  both  sides.  Should  the 
separation  upon  one  side  be  extreme,  it  is  past  correcting, 
and  necessitates  returning  to  the  casts  and  beginning  again. 
As  the  novice  learns  by  experience,  he  will  see  that  equalized 
pressure  is  an  absolute  necessity  in  the  occlusion  and  contour 
models,  and  this  prevents  the  unequal  pressure  in  the  model 
dentures. 

The  model  dentures,  meeting  the  tests  applied  for  retruded 
occlusion  and  equalized  pressure,  are  placed  in  incisal  occlu- 
sion and  tested  with  the  thin  spatula  for  equal  pressure  at  the 
three  points  of  contact.  The  dentures  are  then  consecutively 
placed  in  right  and  left  lateral  occlusion  and  tested  with  the 
spatula.  The  dentures  meeting  these  tests  are  removed 
from  the  mouth,  laved  in  cold  water,  dried,  and  returned  to 
the  antagonizor.  As  slight  imperfections  of  occlusion  and 
antagonization  will  be  unconsciously  corrected  in  the  mouth, 
and  may  be  apparent  upon  the  antagonizor,  it  will  be  neces- 
sary to  bring  the  antagonizor  to  the  proved  model  dentures, 
and  not  the  dentures  to  the  antagonizor.  The  antagonizor 
is  conformed  to  the  tested  model  dentures  in  this  manner. 
The  upper  cast  is  removed  from  the  antagonizor,  the  model 
dentures  and  upper  casts  are  assembled  upon  the  lower 
cast,  and  the  upper  bow  again  attached  to  the  cast  with 


CONVERTING  THE  MODEL  UAHE  INTO  VULCANITE     249 

plaster.  However,  it  is  not  iiece^ssary  to  conform  the  aiitaK- 
oiiizor  to  the  tested  model  dentures  unless  it  is  desirable  to 
make  changes  for  cosmetic  effects;  then  it  is  well  to  have  a 
fixed  record  of  the  antagoni/ation  as  developed  in  the  mouth. 
It  should  })e  evident  to  the  student  that  if  all  the  procedures 
have  been  faultlessly  j)crfornied  up  to  the  mouth  test,  no 
corrections  will  be  necessary;  but  as  there  are  so  many  sources 
for  error,  it  is  necessary  for  the  most  experienced  and  skilful 
prosthetist  to  [)rove  the  work  at  this  staj^c  of  construction. 

The  second  object  of  the  third  ai>i>oiiitni('nt  is  t(j  devcloj) 
the  esthetics.  ''J'his  i)hase  of  the  subjc<-t  will  be  fully  treated 
in  the  chapter  on  esthetics.  The  design  in  this  chapter  is 
to  treat  only  the  art  and  the  science  of  construction. 

CONVERTING  THE  MODEL  BASE  INTO  VULCANITE 

The  model  dentures  having  been  perfected  are  ready  to 
be  converted  into  their  permanent  form.  This  consists  of 
substituting  vulcanite  for  the  wax.  This  conversion  requires 
good  workmanship  and  involves  considerable  science. 

Synopsis.  Luting  the  model  dentures  to  the  casts;  re- 
moving from  antag(jnizor;  flasking;  opening  flask;  removing 
wax;  heating;  packing;  closing  flask;  vulcanizing;  removing 
from  x'ulcanizer  an<l  flask:  finishing. 

Luting.  The  model  dentures  are  luted  to  the  plaster  casts 
by  running  a  hot  wax  spatula  (Fig.  lOo)  along  the  jx-ripheral 
border.  It  is  essential  to  have  the  entire  border  luted  .so  as 
to  prevent  the  soft  flasking  plaster  from  getting  between 
the  inf)dcl  dentures  and  casts. 

Removing  from  Antagonizor,— The  bows  holding  the  casts 
are  removed  from  the  antagonizor  frame.  The  plaster  cast 
is  removed  from  the  bow  by  soaking  in  water  for  a  minute 
or  two,  trimming  away  any  luting  plaster  that  may  over- 
lap the  cast,  forming  a  notch  between  the  cast  and  luting, 
inserting  a  plaster  spatula  in  the  notch,  and  tapping  with  a 
light  hammer. 

Flasking. — The  cast  with  its  luted  model  denture  is  then 
adju-tcd  to  the  vulcanite  flask.     The  adjustment  consi.sts 


250 


RUBBER  AND   VULCANITE 


in  seeing  that  the  cast  is  neither  too  thick  nor  too  wide  for 
the  flask;  if  such  is  the  case,  the  cast  must  be  reduced.  This 
is  done  with  a  plaster  knife  (Fig.  62),  after  soaking  the 
cast  in  water.  Sufficient  soft  mixed  plaster  is  placed  in  the 
lower  half  of  the  flask  to  fill  it  half  full.  The  cast  is  then 
pressed  into  the  soft  plaster  a  sufficient  depth  to  permit  of 
the  teeth  being  clear  of  the  cover  when  the  ring  and  cover 
are  in  place.  Plaster  is  added  to  fill  the  space  between  the 
edge  of  the  base  of  the  flask  and  the  periphery  of  the  model 
denture.  The  plaster  must  not  be  carried  upon  the  model 
denture.  When  the  plaster  has  set  it  is  trimmed  smooth 
with  the  plaster  knife.     Fig.  155  shows  the  case  properly 


Fig.   155 

-iS-'-* 

# 

w 

i 

enclosed  in  the  first  section  of  the  flask.  The  plaster  being 
set  and  trimmed  so  that  no  portion  overlaps  the  rim  of  the 
flask,  a  slope  extending  from  the  model  denture  to  the  rim 
of  the  flask,  and  care  exercised  that  no  form  is  given  to  the 
plaster  to  act  as  a  key  and  thus  interlock  the  two  sections  of 
the  flask,  the  exposed  surface  of  plaster  is  varnished  with 
sandarac  as  a  separator. 

Flasking  Upper  Section. — As  soon  as  the  varnish  has  dried 
the  surface  of  the  porcelain  teeth  and  wax  model  base  is 
wetted  by  holding  in  running  water;  this  will  favor  the  plaster 
flowing  smoothly  over  the  surface  and  filling  the  interspaces 
between  the  teeth.  The  model  denture  being  wetted,  the 
ring  of  the  flask  is  set  in  place  and  a  thick  creamy  mix  of 


CONVERTING  THE  MODEL  BASE  INTO  VULCANITE     251 

plaster  of  Paris  is  poured  in  to  nearly  half  fill  it;  the  base  and 
ring  of  the  flask  are  so  grasped  as  to  hold  them  together 
while  jarring  on  the  bench,  thus  causing  the  plaster  to  settle 
into  every  interspace  between  the  teeth.  ^lore  plaster  is 
added  and  settled  in  place  by  jarring.  The  third  addition 
of  plaster  should  fill  the  ring  when  the  cover  is  placed  and 
firmly  pressed  with  the  finders,  thus  forcing  out  any  excess 
plaster,  which  is  wiped  away. 

Opening  the  Flask. — The  filled  flask  should  stand  until 
the  plaster  is  hard  set  (thirty  minutes).  It  is  then  placed  in 
a  three-quart  stew  pan  and  covered  with  cold  water.  The 
pan  is  placed  upon  the  gas  stove  or  large  laboratory  heater 
and  heated  until  the  water  begins  to  boil,  when  the  flask 
is  removed  from  the  water  (use  flask  tongs,  Fig.  122,  or 
holder  of  Buflalo  No.  2  press,  Fig.  113)  and  held  in  the  left 
hand  protected  with  a  cloth  holder.  Start  the  separation 
of  the  two  sections  of  the  flask  by  inserting  the  edge  of  a 
plaster  knife  between  them.  As  soon  as  the  two  sections 
loosen,  the  upper  section  is  grasped  with  a  cloth  holder  and 
carefully  drawn  apart,  care  being  exercised  to  so  manipulate 
the  two' sections  as  to  release  them  of  any  slight  interlocking. 
The  rule  for  placing  the  knife  for  starting  the  separation  is: 
For  upper  cases  place  the  knife  at  the  heel  of  the  flask,  and 
for  lower  cases  at  the  toe  of  the  flask.  This  will  prevent 
fracturing  the  overhanging  anterior  alveolar  ridge. 

The  instruction  given  for  heating  in  water  is  subject  to 
much  variation.  The  object  is  to  apply  heat  in  such  a  way  as 
to  soften  the  wax  without  melting  it.  It  is  evident  that  some 
judgment  is  necessary,  as  there  are  several  factors,  such  as 
amount  of  heat,  water,  and  plaster  about  the  wax.  A  little 
experience  and  observation  will  enable  the  prosthetist  to 
closely  estimate  the  time  to  open  the  flask. 

Another  method  is  to  have  the  water  boiling  and  submerge 
the  flask  for  three  to  seven  minutes.  The  time  is  inversely 
to  the  thickness  of  the  encasing  plaster  al)()ut  the  wax. 

Removing  Wax.— The  softened  wax  is  removed  from  the 
parted  flask  with  a  wax  spatula  so  far  as  possible,  and  the 
remainder  removed  by  a  stream  of  boihng  water.     (A  small 


252 


RUBBER  AND   VULCANITE 


teakettle  is  excellent  for  this  purpose.)  By  examining  the 
parted  flask  it  will  be  seen  that  the  cast  is  in  the  bottom 
section  of  the  flask,  and  the  teeth,  with  their  cervical  ends 
exposed,  are  in  the  upper  section.  If  any  plaster  has  found 
its  way  about  the  pins  and  cervical  ends  of  the  teeth,  where 
there  should  be  none,  it  should  be  removed  with  a  pointed 
instrument  and  brush. 

Heating. — The  upper  section  of  the  flask  is  placed  upon 
an  8  or  10  inch  square  piece  of  sheet  iron  over  the  gas  stove. 

Fig.  156 


as  shown  in  Fig.  156.  While  inspecting  the  upper  section  of 
the  flask  the  lower  section  is  placed  under  the  sheet  iron,  as 
seen  in  Fig.  156,  to  be  dried  by  reflected  heat.  During  the 
three  or  four  minutes  that  the  upper  section  is  warming,  the 
surface  of  the  cast  in  the  lower  section  of  the  flask  is  given 
attention.  The  surface  of  the  cast  should  be  treated  so  that 
it  will  impart  a  dense  and  smooth  surface  to  the  vulcanite. 
There  are  two  methods  for  accomplishing  this— (1)  painting 
the  surface  with  a  liquid  finish,  and  (2)  covering  with  tinfoil. 


CONVERTING  THE  MODEL  BASE  INTO  VULCANITE     253 

The  Silex  Method.— The  liquid  silex  method  has  the 
advantage  of  being  easily  applied,  and  if  the  surface  of  the 
cast  is  entirely  free  of  wax  or  oily  substances,  will  give  good 
results.  A  clean  ox-hair  or  camel's-hair  brush  is  dipped  into 
the  liquid  silex  and  is  then  applied  to  the  cast.  It  will  be 
necessary  to  occasionally  dip  the  brush  into  water,  so  that 
the  silex  may  be  well  diluted  and  evenly  applied.  The  excess 
silex  should  be  absorbed  with  a  cloth.  Another  method  is 
as  follows:  While  the  thin  silex  is  still  moist  upon  the  cast, 
dust  with  talcum  powder,  and,  when  dry,  rub  carefully  with 
a  soft  cloth.  Liquid  silex  acts  better  on  plaster  of  Paris 
casts  than  en  Spence  plaster  compound  casts.  The  liquid 
silex  bottle  should  be  kept  well  corked  and  no  particles  of 
plaster  be  permitted  to  get  into  it,  as  they  will  precipitate  and 
spoil  the  silex  for  its  intended  use.  The  brush  must  be  well 
washed  each  time  it  is  used. 

The  Tin  Method.— This  method  is  preferable  because  it 
gives  a  smoother  and  denser  surface  to  the  vulcanite,  espe- 
cially if  any  wax  has  been  melted  into  the  cast.  A  sheet  of  No. 
6  or  8  tinfoil  is  fitted  o\er  the  cast  with  the  thumb  and  finger. 
It  is  then  removed  and  the  excess  tin  cut  away  with  sharp 
scissors,  as  indicated  by  the  imprint  of  the  edge  of  the  cast 
upon  the  tin.  The  cast  is  now  coated  with  sandarac  varnish, 
and  the  tin  is  at  once  replaced  and  firmly  pressed  and  gently 
rubbed  with  a  wad  of  soft  paper  until  there  is  perfect  adap- 
tation to  the  cast.  The  tin  should  be  rubbed  until  it  has 
a  well-burnished  surface.  It  is  important  that  the  tinned 
cast  be  coated  with  a  lather  of  soap.  This  is  accomplished 
by  wetting  a  soft  bristle  brush  and  rubbing  it  upon  a  cake 
of  soap  and  then  upon  the  palm  of  the  hand  until  a  smooth 
lather  is  formed,  which  is  applied  to  the  tinned  surface;  or, 
a  thin  wash  of  Johnson's  ethereal  soap  may  be  used.  If  the 
soap  is  not  applied  the  tin  and  vulcanite  will  adhere  very 
stronglx-,  and  can  only  be  separated  by  dissolving  the  tin 
with  mercury  or  hydrochloric  acid. 

The  cast,  having  been  coated  with  either  silex  or  tinfoil, 
is  replaced  under  the  sheet  iron  to  be  warmed  while  packing 
the  rubber  into  the  upper  section  of  the  flask. 


254  RUBBER  AND  VULCANITE 

Packing  the  Rubber. — During  the  time  the  flask  is  being 
heated  preparatory^  to  separating,  the  rubber  is  stripped  of 
its  cloth  covering  and  cut  into  suitable  form  for  packing. 
For  the  upper  case  a  piece  of  red  rubber  is  cut  of  sufficient 
size  to  cover  the  central  portion  between  the  teeth;  and  the 
remainder  of  the  red  rubber,  required  for  either  the  upper 
or  lower,  is  cut  into  strips,  across  the  sheet,  about  one-half 
inch  wide.  Sufficient  pink  rubber,  or  Walker's  granular 
gum,  to  face  the  labial  and  buccal  surfaces  of  the  case  is 
cut  into  the  same  sized  strips,  also  thirteen  small  pieces 
(triangle  or  square,  form  indift'erent,  size  about  one-fourth 
inch)  are  cut  for  packing  between  the  teeth.  For  conveni- 
ence of  handling,  the  cut  rubber  may  be  placed  upon  a  por- 
celain plate  or  a  piece  of  glass.  As  rubber  is  very  cohesive, 
the  pieces  must  not  touch  each  other  while  on  the  receptacle. 
As  the  flask  is  heated,  it  is  unnecessary  to  heat  the  rubber; 
in  fact,  the  cold  rubber  can  be  much  more  conveniently 
handled  than  that  which  is  warm  and  adhesive.  The  heat 
of  the  flask  will  sufficiently  soften  the  rubber  to  cause  it  to 
pack  easily.  Care  should  be  exercised  not  to  overheat  the 
flask.  It  should  be  about  the  temperature  of  boiling  water, 
or  lower.  As  rubber  melts  at  250°  F.,  and  its  quality  is 
impaired  when  melted  if  exposed  to  air,  it  is  well  to  have 
a  safe  margin  of  40°  or  50°.  Two  instruments,  one  in 
each  hand,  will  be  required  for  packing  the  rubber.  Any 
small  and  blunt  instrument  may  be  used.  A  small  flat- 
blade  burnisher  held  in  the  left  hand  to  stay  the  rubber 
while  packing,  also  useful  to  carry  the  small  pieces  between 
the  ends  of  the  teeth,  and  the  No.  3  instrument  of  the  Evans 
set  (Fig.  104)  are  admirably  adapted  as  packing  instruments. 
A  narrow  strip  of  red  rubber  is  placed  along  the  pins  of  the 
teeth,  and  as  the  rubber  softens  is  pressed  against  the  pin 
with  the  flat  side  of  the  broad  end  of  the  No.  3  instrument. 
The  pins  of  all  the  teeth  being  engaged  in  the  red  rubber, 
one  of  the  small  pieces  of  pink  rubber  is  engaged  in  each  of 
the  spaces  between  the  ends  of  the  teeth.  Packing  these 
small  pieces  is  simple  and  expeditious;  however,  a  novice  is 
liable  to  waste  much  valuable  time  in  its  performance.    The 


cox  VERTING  THE  MODEL  BASE  INTO  VULCANITE     255 

small  pieces  of  rubber  are  carried  on  the  pointed  end  of  the 
No.  3  instrument  to  place,  the  edge  of  the  burnisher,  held 
in  the  left  hand,  carries  it  between  the  teeth,  and  while  so 
held  the  No.  3  instrument  is  used  to  turn  one  edge  over 
upon  the  centre  of  the  space  between  the  teeth  and  compress 
the  rubber  while  withdrawing  the  other  instrument.  These 
three  movements  to  each  space  should  be  sufficient.  A  strip 
of  the  pink  rubber,  sufficiently  wide  to  nearly  cover  the 
buccal  and  labial  surfaces  of  the  denture,  is  placed  with  one 
edge  overlapping  the  teeth  for  about  one-half  their  thickness. 
The  fingers  are  then  used  to  compress  the  strip  of  rubber 
down  upon  the  ends  of  the  teeth  and  against  the  sides  of 
the  plaster  mold.  This  act  unites  the  large  strip  and  the 
small  pieces  and  perfectly  forms  them  about  the  cervical 
ends  of  the  teeth.  If  much  restoration  is  required  for  the 
gum  portion,  another  layer  of  pink  rubber  may  be  placed 
upon  the  adjusted  piece.  However,  the  edge  of  this  piece 
should  not  overlap  the  teeth,  but  extend  from  the  teeth  to 
the  margin  of  the  mold.  If  there  is  great  thickness  of  gum 
restoration  required,  pink  rubber  should  be  added  to  nearly 
complete  it.  The  reason  for  making  heavy  restorations  with 
pink  rubber  in  place  of  the  stronger  red  rubber  is:  There 
is  no  danger  of  thick  masses  of  pink  rubber  vulcanizing 
porous,  while  the  same  space  filled  w^ith  red  rubber  is  almost 
certain  to  do  so.  If  a  thin  gum  restoration  is  required,  one 
layer  of  pink  is  sufficient.  The  next  step  in  packing  the 
upper  case  is  to  place  the  centre  piece,  which  is  done  by 
adapting  the  piece  of  rubber  to  the  plaster  matrix  by  finger 
pressure,  from  the  centre  outward,  permitting  the  edge  to 
overlap  the  packed  rubber.  In  the  lower  case  one  or  two 
thicknesses  of  red  rubber  is  j)laced  upon  the  lingual  surface 
of  the  mold.  The  packing  of  rubber  is  done  with  the  fingers 
when  possible,  only  using  instruments  where  the  fingers 
cannot  effectively  reach.  The  problem  confronting  the 
workman  at  this  stage  of  the  o])eration  is  to  know  when 
sufficient  rubl)er  has  been  j)laced  to  just  fill  the  mold,  for 
much  excess  rubber  is  liable  to  do  harm.  Various  methods 
are  u.sed,  as:  Weighing  the  wax  model  plate  and  taking  its 


256  RUBBER  AND   VULCANITE 

weight  plus  one-fifth  in  rubber,  the  difference  in  specific 
gravity.  Displacement  method:  Place  the  wax  model 
plate  in  a  suitable  dish  (glass  tumbler)  and  fill  it  to  over- 
flowing with  water;  the  wax  is  removed  and  replaced  with 
rubber.  With  either  of  these  methods  a  little  extra  rubber 
should  be  added  and  good  judgment  used  in  distributing 
the  rubber  in  packing.  The  preferred  method  is  the  "Trial" 
method. 

Closing  the  Flask. — -This  (trial)  method  consists  of  placing 
the  rubber  in  the  mold  as  has  been  described,  until  the  judg- 
ment dictates  there  is  nearly  but  not  enough  to  fill  the  mold. 
A  piece  of  close  woven  cotton  cloth  free  from  starch  is 
saturated  with  water  (preferably  hot)  and  placed  over  the 
packed  rubber,  the  two  sections  of  the  flask  are  put  together 
and  carefully  closed  in  the  flask  press.  The  flask  is  then 
opened  and  the  cloth  removed,  when  it  will  be  apparent 
where  more  rubber  is  required  and  the  quantity.  Should  so 
large  a  quantity  of  rubber  be  required  that  it  is  questionable 
when  a  sufficiency  has  been  added,  a  trial  with  the  wet  cloth 
may  again  be  made.  When  the  mold  is  found  to  be  full,  the 
flask  is  closed  without  the  cloth.  (The  cloth  stripped  from 
the  rubber  and  washed  of  its  starch  may  be  used,  but  silesia 
cut  in  pieces  3  by  3^  inches  is  better  and  saves  valuable 
time.  Should  the  cloth,  for  any  reason,  adhere  to  the  rubber, 
saturate  it  with  hot  water,  when  they  may  be  easily  parted.) 
Attention  has  been  called  (page  204)  to  the  danger  of  warping 
the  denture  by  improper  placing  of  the  rubber  and  heavy 
pressure  in  the  press.  Should  the  rubber  in  the  mold  become 
too  cold,  it  may  be  warmed  by  reflected  heat  under  the 
sheet  iron.  In  no  case  should  the  rubber-packed  flask  be 
put  in  water  and  boiled  before  the  final  compression  in  the 
press,  as  the  softening  that  takes  place  in  the  saturated 
plaster  favors  warping  the  denture.  Undoubtedly  the  "fit" 
of  more  artificial  dentures  is  impaired  by  improper  packing 
and  closing  the  fiask  than  by  all  other  causes.  The  fiask 
being  closed  is  bolted  or  placed  in  a  Donham  clamp  (Fig. 
109). 


COXVERTIXG  THE  MODEL  BASE  INTO  VULCANITE     257 

Vulcanizing. — For  convenience,  cleanliness,  and  uniformity 
of  results,  dental  vulcanization  is  accomplished  in  a  specially 
constructed  machine  called  a  vulcanizer  (Fig.  121),  which 
is  a  steam-tight  boiler.  The  operation  can  be  accom- 
plished in  a  sand,  glycerin,  or  oil  bath,  but  this  is  not 
desirable  for  obvious  reasons.  The  time  of  vulcanizing  will 
be  influenced  by  both  temperature  and  the  surrounding 
medium.  Vulcanization  begins  at  248°  F.,  but  at  that 
temperature  it  would  require  many  hours;  at  280°  F.,  it 
will  require  five  and  one-half  hours;  at  300°  F.,  two  and  one- 
half  hours;  and  at  320°  F.,  fifty  minutes.  The  medium 
surrounding  the  flask  in  the  vulcanizer  must  be  either 
water,  steam,  or  air.  The  time  required  to  produce  the 
same  results  will  be  in  inverse  ratio  to  the  conducting  power 
of  the  medium;  water,  being  the  best  conductor  of  heat,  will 
require  the  least  time,  steam  second,  and  air,  being  the  poorest 
conductor,  will  require  the  longest  time.  The  vulcanizing 
process  consists  of  causing  the  mechanical  mixture  of 
caoutchouc  gum  and  sulphur  to  combine  chemically.  This 
is  accomplished  by  the  action  of  heat.  As  there  are  various 
compounds  formed,  varying  from  CiooHjcoS,  for  the  lowest 
combination,  to  CioHisSo,  as  the  highest,  it  is  evident  that 
the  degree  of  heat  and  the  length  of  time  the  heat  is  applied 
are  the  essential  factors  in  producing  these  compounds;  and 
as  there  are  two  chemical  processes  going  on,  the  addition  and 
the  substitution,  the  manner  of  the  application  of  the  two 
factors  will  determine  the  quality  of  the  product  produced. 
The  evolution  of  gas,  H2S  (see  page  196),  may  do  much  harm 
if  not  properly  controlled.  Therefore  it  is  evident  that  the 
best  conductor  of  heat  (water)  will  give  the  most  equitable 
temperature  and  is  the  preferred  medium;  and  that  the 
temperature  and  time  should  be  governed  by  the  thickness 
of  the  mass  of  rubber  to  be  converted  into  vulcanite.  A 
thin  sheet  of  rubber  may  be  vulcanized  rapidly,  that  is,  at 
a  high  temperature  (320°  F.)  and  short  time,  that  is,  eighty 
minutes — thirty  minutes  to  "  heat  up,"  and  that  temperature 
maintained  for  fifty  minutes.  Rubber  one-fourth  inch  thick 
may  be  heated  to  300°  F.  in  thirty  minutes  and  maintained 
^7 


258  RUBBER  AND  VULCANITE 

at  that  temperature  for  two  and  one-half  hours.  A  mass  of 
rubber  one-half  inch  thick  should  not  be  heated  above 
280°  F.,  but  that  temperature  should  be  maintained  for  six 
hours.  Therefore  a  good  rule  is:  Thin  pieces  of  rubber,  as 
base-plates,  vulcanize  at  320°  F.,  time  eighty  minutes;  thick 
cases,  temperature  300°  F.,  time  three  hours.  However,  with 
thick  cases  the  temperature  may  be  raised  and  the  time 
shortened  by  using  pink  rubber  (because  of  its  contained 
earthy  matter)  upon  a  thin  sheet  of  red  or  black  rubber. 

Removing  from  the  Vulcanizer. — It  is  always  best  to  permit 
the  vulcanizer  to  stand  until  it  is  cold  before  opening,  but 
when  it  is  necessary  to  expedite  matters,  the  steam  may  be 
blown  off,  the  vulcanizer  opened,  and  the  flask  submerged 
in  a  pan  of  cold  water.  This  last  procedure  would  be  con- 
demned by  some,  but  owing  to  the  poor  conducting  and 
radiating  property  of  plaster,  it  is  doubtful  if  this  method  of 
cooling  ever  accounts  for  fractured  teeth. 

Rertioving  from  the  Flask. — Under  no  conditions,  however, 
should  the  flask  be  opened  until  the  plaster  in  the  centre  of 
the  flask  is  cooled  to  blood  heat,  which  will  be  some  time 
after  the  flask  is  cold  if  placed  in  water,  The  flask  is  released 
of  its  clamp  or  bolts,  held  in  the  left  hand,  with  the  plaster 
knife  in  the  right  hand.  The  knife,  guarded  with  the  thumb 
so  that  only  a  quarter  or  half-inch  is  exposed,  is  used  as  a 
wedge  to  part  the  sections  of  the  flask.  Usually  the  case  will 
remain  in  the  ring  portion  of  the  flask,  and  is  removed  by 
cutting  a  groove  in  the  encasing  plaster  between  the  denture 
and  ring.  The  plaster  both  on  the  inside  and  outside  of  the 
denture  is  grooved  and  removed  in  sections,  thus  avoiding 
the  danger  of  fracturing  the  denture.  The  last  portions  of 
the  plaster  not  easily  removed  with  the  knife  are  removed 
by  scrubbing  with  a  stiff  bristle  laboratory  brush  and  water. 

Finishing. — The  edges  of  the  denture  as  it  comes  from  the 
flask  are  rough  and  irregular  from  the  extension  of  excess 
vulcanite.  This  is  removed  with  a  rather  coarse  file  spe- 
cially made  for  this  work  (Fig.  123).  A  seven  or  eight  inch 
half-round  file,  having  an  oval  and  a  flat  side,  a  coarse 
and  a  fine  end,  is  a  very  desirable  instrument.    The  cutting 


CONVERTING  THE  MODEL  BASE  INTO  VULVANITE     259 

is  done  with  a  push  stroke.  A  round  or  rat-tail  file  is  also 
very  useful.  For  scraping  the  surfaces  the  Xo.  1  short 
shank  Kingsley  scraper  of  the  Wilson  vulcanite  finishers  is 
used.  The  No.  4  instrument  is  useful  for  small  places,  and 
especially  for  removing  defects  on  the  maxillary  and  man- 
dibular surfaces.  The  chisel  (No.  2  of  this  set)  is  for  carving 
about  the  teeth,  and  the  pick  (No.  3)  is  for  working  between 
the  teeth  (Fig.  124).  These  instruments  should  be  kept 
very  sharp  by  grinding  and  honing.  The  entire  labial, 
buccal,  and  lingual  surfaces  of  both  upper  and  lower  den- 
tures are  gone  over  to  remove  excess  material,  give  form, 
and   to  remove  the  roughness  received   from   the  plaster 

Fig.   157 


matrix.  The  file  and  scraper  marks  are  removed  with  sand- 
paper. No.  5  for  coarse  paper  and  No.  00  for  fine  paper  is  cut 
into  two  and  one-half  inch  squares,  by  placing  the  sand  side 
down  over  a  crevice  and  cutting  with  a  knife.  The  sand- 
paper marks  are  removed  with  bufi'ers  and  glossers  (see  pages 
224  to  229).  The  maxillary  and  mandibular  surfaces  require 
no  finishing  except  to  remove  any  excrescences  formed  as  a 
result  of  air  bubbles  in  the  surface  of  the  cast.  These  are 
carefully  removed  with  the  small  scraper.  This  surface 
may  be  more  highly  glossed  by  using  the  soft  brush  wheel 
and  whiting.  The  finish  grinding  (see  page  2'M))  of  the  occlusal 
surface  of  the  teeth  is  executed  with  small  stones  mounted 


260  RUBBER  AND  VULCANITE 

on  an  engine  mandrel  and  carried  in  the  lathe  chuck.  The 
object  sought  is  to  deepen  or  reproduce  the  sulci  and  grooves, 
thus  forming  egdes  to  cut  the  food  in  the  process  of  masti- 
cation. The  ground  surfaces  of  the  porcelain  teeth  are  given 
their  final  finish  with  a  piece  of  No.  00  sandpaper  applied  with 
the  ball  of  the  thumb.  The  finishing  of  any  mechanical 
work  is  an  important  item,  and  in  artificial  dentures  is  not 
only  indicative  of  superior  workmanship,  but  is  necessary 
for  cleanliness  and  health  of  the  tissues  with  which  it  will 
be  in  contact.    Fig.  157  illustrates  the  completed  dentures. 

Inserting  the  Finished  Dentures. — The  fourth  appointment 
with  the  patient  is  a  very  important  one.  The  dentures  are 
inserted  and  the  adaptation  in  every  respect  inspected. 
The  dentures  are  wonted  to  their  place  by  closing  the  teeth 
and  swallowing;  this  settles  and  withdraws  the  air  from 
beneath  them.  If  the  dentures  are  evenly  seated,  so  that 
pressure  may  be  made  upon  any  part  without  being  dis- 
turbed when  opening  the  mouth  and  by  the  ordinary  move- 
ments of  the  lips  and  tongue,  and  do  not  cause  pain,  and 
the  occlusion  and  antagonization  are  correct,  the  patient 
should  be  instructed  how  to  use  and  cleanse  them.  The 
patient  should  be  instructed  to  keep  the  dentures  in  night 
and  day,  only  removing  for  cleansing,  until  they  have 
become  masters  of  the  artificial  substitutes,  after  which  the 
dentures  should  be  removed  at  night,  cleansed,  and  kept 
in  a  weak  solution  of  boracic  acid.  The  patient  should  be 
instructed  that  if  the  dentures  cause  pain,  they  are  not  to 
be  removed,  but  that  the  patient  is  to  return  to  the  office 
for  attention. 


THE  CONSTRUCTION  OF  EITHER  AN  UPPER  OR  LOWER 

DENTURE 

The  technique  involved  in  the  construction  of  either  an 
upper  or  lower  denture  varies  from  that  of  both  upper  and 
lower  in  a  few  of  the  processes.  As  the  technique  for  con- 
structing an  upper  denture  to  natural  lower  teeth  is  the  same 


CONSTRUCTION  OF   UPPER  OR  LOWER  DENTURES    261 

as  constructing  a  lower  denture  to  natural  upper  teeth,  or 
vice  versa,  it  is  necessary  to  describe  but  one,  as  the  descrip- 
tion of  either  would  be  the  same  as  the  other  except  in  the 
use  of  the  terms  upper  and  lower,  which  would  be  transposed. 
For  convenience  of  description  the  imaginary  patient  has  an 
edentulous  upper  jaw  with  a  full  complement  of  normally 
aligned  lower  teeth. 

The  mouth  is  carefully  examined  and  the  conditions 
observed.  A  scheme  is  devised  for  taking  the  impression 
according  to  the  indications,  a  suitable  cast  and  the  uppei 
occlusion  and  contour  model  formed.  The  processes  of  con- 
struction are  the  same  as  described  for  the  complete  upper  and 
lower  case  up  to  forming  the  occlusal  surface  of  the  wax  model. 
As  in  the  former  case,  the  occlusal  surface  of  the  anterior 
portion  of  the  model  must  mark  the  length  of  the  upper  lip 
when  at  rest  and  relaxed.  The  occlusal  surface  of  the  model 
as  it  extends  backward  must  have  at  least  three  widely 
separated  points  of  contact  with  the  lower  teeth.  The 
patient  is  then  exercised  in  the  forward  and  backward  or 
protrusion  and  retrusion  movements  of  the  mandible.  The 
wax  model  is  then  removed  from  the  mouth,  cooled,  and 
dried.  With  a  roll  of  soft  wax  placed  upon  the  occlusal 
surface  of  the  model,  it  is  returned  to  the  mouth,  and  the 
mouth  closed  in  the  retruded  position,  biting  the  teeth 
through  the  soft  to  the  hard  wax.  The  wax  model  is  removed 
from  the  mouth  and  a  wax  impression  taken  of  the  lower 
teeth.  The  imprint  of  the  lower  teeth  in  the  wax  model 
will  not  suffice  for  the  impression.  The  wax  impression  is 
taken  by  placing  a  roll  of  well-softened  yellow  wax  in  a 
warmed,  suitable  size,  flat  floor  lower  tray.  A  good  imj)res- 
sion  should  be  obtained  of  the  occlusal  surfaces  and  at  least 
one-half  of  the  length  of  the  teeth.  The  impression  of  the 
cervical  half  of  the  teeth  is  indifferent.  The  impression  is 
filled  with  plaster  or,  better,  Spence  compound.  When  the 
plaster  is  hard  set,  the  tray  is  removed  by  warming  in  the 
Bunsen  flame  and  lifting  it  away  from  the  wax.  The  wax 
will  be  somewhat  softetuid  in  removing  the  tray,  and  may 
be  further  softened  by  passing  through  the  flame.     It  is 


262  RUBBER  AND   VULCANITE 

removed  from  the  cast  by  turning  the  buccal  and  labial 
surfaces  of  the  wax  upward  and  inward  to  the  lingual  side, 
when  it  may  be  easily  removed  from  the  cast.  The  upper 
cast,  wax  occlusion  model,  and  lower  cast  are  then  assembled 
and  mounted  upon  an  occlusion  frame  or  an  antagonizor 
to  be  used  as  an  occlusion  frame.  The  student  should  be 
impressed  with  the  fact  that  the  casts  so  mounted  are  in  no 
way  to  have  their  relationship  changed  without  removing 
from  the  frame  and  remounting.  It  is  hardly  necessary  to  use 
a  face  bow  in  mounting  a  single  case  upon  an  antagonizor, 
as  the  occlusion  is  established,  and,  except  in  rare  cases,  it  is 
not  justifiable  to  alter  these  natural  teeth.  However,  the 
face  bow  may  be  used  if  desired,  in  the  same  manner  as  for 
the  full  upper  and  lower  dentures.  A  case  so  mounted 
permits  of  opening  or  closing  the  bite,  but  this  will  not  be 
necessary  if  proper  attention  was  given  to  forming  the  wax 
model.  Then,  again,  if  the  case  is  mounted  with  the  face 
bow,  interfering  cusps  may  be  more  easily  detected. 

The  teeth  must  be  ground  and  set  up  so  that  the  molars 
and  biscuspids  intercuspate  and  the  six  anterior  teeth  are 
free  of  contact.  As  it  is  a  rare  instance  that  a  full  upper 
denture  will  be  required  and  the  patient  have  a  full  set  of 
normally  aligned  natural  lower  teeth,  it  becomes  necessary 
to  give  special  attention  to  the  occlusion.  The  law  of  fcrce 
and  the  law  of  the  resultant  of  two  or  more  forces  must  be 
taken  into  consideration,  or  the  completed  denture  will  be 
very  deficient.  The  rule  is  to  have  the  force  or  the  resultant 
of  two  forces  act  at  right  angles  to  the  normal  occlusal 
plane.  However,  it  is  permissible  and  often  desirable  to 
have  the  line  of  force,  acting  upon  a  full  upper  artificial 
denture,  slightly  distal  to  the  perpendicular.  This  is  accom- 
plished by  having  a  greater  stress  upon  the  mesial  than  upon 
the  distal  facets  of  the  upper  teeth.  The  teeth  being  properly 
occluded  (leaving  the  antagonization  to  be  attended  to  at 
the  time  of  fitting  in  the  denture),  the  construction  is  com- 
pleted the  same  as  in  the  case  previously  described. 


PARTIAL  DENTURES  ON  VULCANITE  BASE      263 


PARTIAL  DENTURES  ON  VULCANITE  BASE 

It  is  a  truism  that  the  difficulties  of  constructing  arti- 
ficial dentures  are  in  direct  ratio  to  the  number  of  teeth  to  be 
supplied.  The  technique  of  constructing  a  partial  vulcanite 
denture  for  either  jaw  is  the  simplest  prosthetic  procedure 
(however,  the  fitting  in  or  adjusting  to  the  mouth  is  more 
difficult  than  any  other  vulcanite  denture);  either  a  full 
upper  or  lower  is  more  complicated,  while  the  complete 
upper  and  lower  present  the  greatest  problems  of  prosthesis. 

A  perfect  plaster  impression  (see  Chapter  II)  should  be 
obtained  to  enclose  a  little  larger  surface  than  the  base- 
plate is  designed  to  cover.  Usually  an  occlusion  cast  of  the 
opposite  teeth  is  required;  however,  if  there  are  no  opposing 
teeth  an  occlusion  cast  will  not  be  necessary.  In  some  partial 
cases  the  two  casts  will  have  so  many  points  of  contact  that 
they  may  be  assembled  without  further  aids.  A  quash-bite 
will  suffice  for  some  cases,  while  for  others  a  well-constructed 
occlusion  wax  model  may  be  a  necessity.  The  case  is  placed 
in  an  occlusion  frame,  a  wax  base-plate  formed,  teeth  of 
color,  form,  and  size  to  correspond  with  the  remaining  teeth 
in  the  mouth  are  selected.  They  may  be  ground  to  favor 
adjustment,  also  to  obtain  the  required  occlusion.  It  is  rarely 
necessary  or  advisable  to  try  a  partial  model  artificial  den- 
ture in  the  mouth.  The  wax  model  plate  being  contoured,  the 
cast  containing  it  is  removed  from  the  occlusion  frame.  The 
rule  for  flasking  full  cases  is:  The  separation  of  the  two 
sections  should  be  at  the  peripheral  edge  of  the  wax  model 
plate.  This  rule  applies  to  some  partial  cases.  In  these 
cases  the  plaster  teeth  should  be  cut  down  flush  with  the 
wax  model  plate  and  the  encasing  plaster  built  up  to  the  top 
of  the  stumps  of  the  plaster  teeth.  These  reenforced  stumps 
must  be  so  shaped  that  they  will  easily  draw  from  the 
mortise  they  form  in  the  upper  section  of  the  flask.  There 
are  many  partial  cases  in  which  the  porcelain  and  ])laster 
teeth  so  alternate  that  it  is  better  to  encase  the  teeth  in 
the  first  secti(Mi  of  the  flask.     It  is  obvious  that  the  packing 


264 


RUBBER  AND  VULCANITE 


of  such  a  case  must  be  from  the  Ungual  aspect.     Fig.  158 
illustrates   an   upper    model   denture   without  labial   gum 


Fig. 

158 

y 

^ 

^~^ 

•\ 

^ 

c^ 

9 

; 

jto^^ 

si  ,4^ 

r 

%%»■ 

4 

J^ 

J 

Fig.  159 


restoration.    Fig.  159  is  the  case  in  the  first  section  of  the 
flask. 


REMOVIXG  TEETH  FROM  VULCANITE  BASE-PLATE   265 

The  tinfoil  used  to  finish  the  maxillary  or  mandibular 
surface  is  applied  before  placing  the  base-plate  wax,  because 
it  will  be  difficult  to  adapt  the  foil  in  the  flask.  The  soap 
solution  is  applied  after  the  wax  is  removed,  just  prior  to 
packing.  Careful  manipulation  will  be  required  in  the 
various  procedures  not  to  disturb  the  finishing  tin.  The 
liquid  silex  method  is  useful  in  many  partial  cases. 

Most  partial  cases  may  be  vulcanized  at  the  high  temper- 
ature (320°  F.)  and  the  short  time,  because  of  the  small 
amount  of  rubber. 

Care  should  especially  be  exercised,  in  removing  the  case 
from  the  flask,  to  have  the  plaster  cold,  and  in  the  use  of 
force. 

The  finishing  process  consists  of  filing,  sandpapering, 
buffing,  and  glossing,  and  are  essentially  the  same  as  for 
full  cases. 

Adapting  the  finished  cases  to  the  mouth  is,  as  has  been 
stated,  a  difficult  and  often  a  perplexing  operation.  It  will 
frequently  require  careful  study  and  manipulation,  and  often 
much  trimming  away  of  the  base-plate  as  formed.  However, 
this  trimming  must  be  judiciously  performed,  because  as 
close  an  adaptation  and  as  large  a  base  of  support  as  possible 
is  imperative.  Partial  cases  may  require  a  high  degree  of 
mechanical  ability,  but  complete  dentures  will  require 
mechanical  dexterity  and  esthetic  sense. 

The  retention  of  artificial  dentures  has  not  been  mentioned 
in  discussing  the  technique  of  vulcanite  construction,  for 
the  subject  is  more  comprehensible  when  considered  in  the 
abstract. 


REMOVING  THE  TEETH  FROM  A  VULCANITE  BASE- 
PLATE 

Sheet  Iron  Method. — Place  the  denture,  teeth  downward, 
ui>on  the  sheet  iron  over  a  gas  stove,  and  when  the  vulcanite 
is  thoroughly  softened,  the  teeth  may  be  pushed  oft'  one  at 
a  time  by  inserting  the  wax  spatula  between  the  tooth  and 


266  RUBBER  AND   VULCANITE 

the  vulcanite  upon  the  Ungual  side.  The  plate  is  held  by  a 
pair  of  pliers  and  the  dislodged  teeth  are  permitted  to  fall 
upon  wood,  or  better,  upon  cloth,  but  not  upon  cold  iron 
or  stone.  Any  portion  of  the  vulcanite  remaining  about  the 
pins  should  be  removed.  If  necessary,  these  small  portions 
of  vulcanite  may  be  softened  by  grasping  the  tooth  in  a 
pair  of  solder  tweezers  and  holding  in  the  Bunsen  flame. 

Glycerin  Method. — The  denture  is  placed  in  a  vessel  of 
glycerin  and  heated  to  the  boiling  point  of  the  liquid,  when 
the  teeth  can  be  removed  as  in  the  other  method.  The 
glycerin  is  soluble  in  water  and  easily  removed.  The  fumes 
of  the  heated  glycerin  are  more  objectionable  to  some  than 
those  of  the  overheated  rubber. 

Flame  Method. — The  denture  is  grasped  with  a  pair  of 
pliers  and  the  outer  surface  of  the  teeth  heated  by  passing 
repeatedly  through  the  flame  until  the  vulcanite  is  softened 
about  the  pins,  when  they  are  removed  as  before  described. 

It  is  not  advisable  to  remove  the  teeth  b.y  heat  from  a 
denture  which  is  to  be  used  again,  because  of  the  liability 
of  warping  the  plate.  In  such  cases  the  vulcanite  should 
be  cut  from  about  the  pins  of  the  tooth  with  a  bur  in  the 
engine,  or  with  a  chisel. 


REPAIRING  VULCANITE  DENTURES 

The  breaking  of  vulcanite  dentures  is  usually  due  to  over- 
vulcanizing,  by  which  elasticity  and  toughness  are  destroyed ; 
to  improper  arrangement  of  the  molars,  by  which  the  strain 
of  mastication  is  thrown  on  the  outside  instead  of  on  top 
of  the  ridge;  or  to  a  warped  plate.  The  first  evidence  of  the 
giving  way  of  a  piece  is  usually  a  fine  crack  appearing 
between  the  two  central  incisors,  and  sometimes,  in  partial 
dentures,  in  the  border  surrounding  a  natural  tooth. 

Wax  Method. — A  method  particularly  applicable  to  plates 
which  are  broken  entirely  in  two,  consists  in  adjusting  the 
two  parts  of  the  plate  together,  and  fastening  them  in  correct 
relation  to  each  other  temporarily  by  adhesive  wax  dropped 


REPAIRING  VULCANITE  DENTURES 


267 


on  the  lingual  surface  until  plaster  can  be  run  into  the 
maxillary  portion  of  the  denture.  As  soon  as  the  plaster 
hardens,  the  plate  is  removed  from  the  cast,  the  line  of 
division  is  enlarged  with  a  file,  and  dovetails  cut  opposite 
each  other  with  a  jeweller's  saw,  as  shown  by  Fig.  100.  The 
dovetailed  space  is  then  filled  with  wax,  invested  in  the  usual 
way  in  a  flask,  packed,  and  vulcanized.  By  another  method 
the  edges  may  be  adjusted  as  before  described,  and  the 
piece  be  placed  immediately  in  the  lower  half  of  the  flask. 
After  the  plaster  has  set,  the  adhesive  wax  is  to  be  removed 
from  the  lingual  side  of  the  plate  and  a  line  cut  with  a  round 

Fig.   160 


engine  bur  along  the  full  extent  of  the  crack,  or  break,  half-way 
through  the  plate  and  a  quarter  of  an  inch  wide,  with  smooth 
regular  edges,  without  dovetails.  The  case  is  then  waxed 
up  and  the  other  half  of  the  flask  poured,  when  the  case  is 
packed  and  vulcanized.  If  the  parts  have  been  kept  per- 
fectly clean,  the  union  will  be  quite  strong. 

Another  modification, ^  which  gives  the  best  results,  is 
this:  After  the  cast  is  made,  the  portions  of  the  plate  are 
removed  from  the  cast  and  with  file  and  scraper  a  long  bevel 
is  cut,  forming  a  thin   feathery  edge  along  the  fractured 


'  The  irii.'thocl  fj  refer  red  by  the  writer. 


268 


RUBBER  AND   VULCANITE 


edge  and  sloping  away  from  this  for  an  eighth  to  one-half 
inch  as  the  case  will  permit  (Fig.  161).  The  pieces  are  then 
filed  to  give  a  slight  bevel  upon  the  maxillary  surface.  The 
portions  of  the  plate  which  have  been  cut  away  are  replaced 
with  wax,  and  if  necessary  the  plate  may  be  thickened  over 
the  portion  having  the  freshly  cut  surface.    It  is  unnecessary 


Fig.  101 


! 

■ 

^Hf'^'-'- 

I^H 

^^^^^^K^  *'^^^l 

f 

W 

Whm 

1,9 

^B  '^  S.:. 

«^H^ft        ■H 

^.--^^      »■.,-; 

,.^- 

^'^^H^i^fli 

■2 

■ 

fe 

^91 

to  coat  the  vulcanite  surface,  with  a  solution  of  rubber,  as 
the  heat  and  pressure  will  make  the  union.  Fig.  162  shows 
method  of  flasking. 

In  this  connection,  attention  is  called  to  a  class  of  repair 
cases  that  perplex  the  novice;  namely,  those  having  an  ex- 
tensive fracture  upon  both  the  lingual  and  buccal  or  labial 
surfaces.  This  difficulty  in  flasking  is  overcome  by  attaching 
one  or  more  shafts  of  wax,  one-fourth  inch  in  diameter,  at 
suitable  locations  over  the  fracture  upon  the  labial  or  buccal 
surface.     The  shaft  of  wax  must  be  suSiciently  long  to 


REPAIRING  VULCANITE  DENTURES 


269 


extend  through  the  investing  plaster.  When  the  plaster  has 
hardened,  a  portion  of  the  wax  shaft  and  the  surrounding 
plaster  is  cut  away  to  form  a  cone-shaped  depression,  which 
vnW  be  filled  in  with  the  plaster  in  the  top  section  of  the 
flask.  These  wax  shafts  will  form  openings  through  which 
the  rubber  can  be  packed,  and  which  are  to  be  filled  with 
rubber.  After  vulcanization  the  shaft  of  rubber  may  be 
removed  with  a  mechanical  saw  (Figs.  161  and  162). 

Fig.   162 


Fusible  Metal  Method. — To  avoid  loss  of  strength  by  the 
seccjud  vulcanizing  it  is  recommended  that  fusible  metal, 
melting  at  I'Af  to  H)()°  F.,  be  used  to  fill  the  dovetail  space. 
This  can  be  done  by  pouring  the  melted  alloy  into  the  space 
and  packing  it  with  a  hot  spatula,  which  is  readily  admissible 
(jwing  to  the  low  fusing-point  of  the  metal.  While  the 
method  has  the  advantage  of  not  requiring  a  second  vul- 


270  RUBBER  AND   VULCANITE 

canizing,  the  union  of  the  metal  at  the  point  of  fracture  is 
not  as  close  as  when  rubber  is  used,  and  it  cannot  be  said  to 
be  reliable  as  a  means  of  repairing  broken  vulcanite  plates. 

A  single  tooth  may  be  fastened  to  the  vulcanite  by  filing 
the  dovetailed  space  as  for  repairing  with  rubber,  the  fusible 
metal  to  be  put  in  place  with  a  hot  spatula;  or  the  dovetail 
can  be  filled  with  amalgam. 

Replacing  Vulcanite  Method. — Much  the  better  way  is  to 
fasten  the  parts  together,  run  a  plaster  cast  into  the  denture, 
then  make  a  bite  of  plaster  to  serve  as  a  guide  for  the  replace- 
ment of  the  teeth,  remove  the  latter  from  the  broken  plate, 
reset  them  to  the  cast,  wax  up  the  piece,  flask,  and  vulcanize. 
This  affords  practically  a  new  case,  and  the  time  consumed 
is  not  much  greater  than  is  required  in  repairing  the  old  one. 

Fig.   163 


Plate  prepared  for  the  addition  of  several  teeth. 

Additions  to  Old  Plates. — Additions  of  teeth  to  old  plates 
are  accomplished  after  practically  the  same  methods.  Fig. 
163  shows  a  case  where  six  teeth  have  been  extracted,  and 
the  old  plate  is  prepared  for  the  addition  of  as  many  por- 
celain teeth,  so  that  the  denture  could  be  worn  until  the 
resorption  of  the  alveoli  and  gums  would  admit  of  the 
construction  of  a  permanent  plate.  The  illustration  shows 
the  plate  bevelled  off  to  a  smooth  edge,  and  several  holes 


REPAIRING   VULCANITE  DENTURES  271 

drilled  into  the  filed  jiortion.  The  correct  occlusion  of  the 
new  teeth  is  obtained  by  placing  the  plate  in  the  mouth 
after  the  bleeding  ceases,  placing  two  pieces  of  softened  wax 
along  the  alveolar  ridge  and  plate,  and  directing  the  patient 
to  bite  into  the  wax,  and  then  gently  pressing  the  wax  while 
the  teeth  are  in  contact.  This  gives  the  correct  relation  of 
the  lower  to  the  upper  teeth,  and  the  impression  of  that 
portion  of  the  alveolar  ridge  to  be  covered  by  the  addition 
to  the  plate.  The  preparation  of  the  plaster  cast  and  bite 
is  done  in  the  usual  way,  plain  teeth  being  ground  to  the 
gums  to  allow  for  the  rapid  resorption  which  always  follows 
the  extraction  of  teeth.  The  waxing  and  flasking  are  done 
in  the  usual  way. 

Ironing-in  Method. — This  method  is  suitable  for  replacing 
a  tooth  or  two,  or  filling  a  short  crack  or  a  hole.  The  vul- 
canite is  cut  with  a  file  to  give  a  dovetailed  form  to  the 
space  into  which  a  tooth  is  to  be  added;  and  a  crack  or 
hole  should  be  prei)ared  for  the  new  rubber  with  a  scraper. 
The  new  rubber  is  ironed  into  place  by  using  a  hot  wax 
spatula  and  firm  pressure. 


CHAPTER  VII 

PRINCIPLES  OF  RETENTION  OF  ARTIFICIAL  DENTURES 

The  retention  of  artificial  dentures  is  purely  mechanical, 
and  is  based  upon  the  laws  of  physics.  Indirectly,  however, 
the  personal  equation  is  an  important  factor,  in  that  the 
patient  may  not  be  able  to  control  the  laws  of  physics. 
These  vexatious  cases  are  often  spoken  of  as  awkward  or 
clumsy,  but  such  patients  will  eventually  succeed  in  over- 
coming the  difficulties,  provided  they  have  sufficient  perse- 
verance. 

The  physical  laws  that  play  a  more  or  less  important 
role  in  the  retention  of  artificial  dentures  are  atmospheric 
pressure,  adhesion  by  contact,  leverage,  tensofriction,  and 
cementation.  These  forces  are  not  equal  in  value,  nor  can 
any  one  principle  be  depended  upon  for  retaining  a  denture. 
There  will  be  a  primary  selected  to  bear  the  burden,  and  one 
or  more  secondary  forces  evoked  or  unwittingly  included. 
These  secondary  forces  may  be  either  positive  or  negative. 
Thus  atmospheric  pressure  may  be  selected  as  the  primary 
retentive  force,  but  adhesion  by  contact  must  be  an  asso- 
ciate retentive  force,  whether  it  be  so  designed  or  net,  and 
eventually  will  entirely  take  the  place  of  atmospheric 
pressure  in  any  given  case.  The  principle  of  leverage  is 
always  associated,  through  antagonization,  with  whatever 
may  be  the  primary  method  selected.  This  force  especially 
may  be  considered  as  positive  when  the  arrangement  of  the 
teeth  is  such  that  it  tends  to  force  the  denture  more  securely 
to  place,  and  as  negative  when  the  arrangement  is  such 
that  antagonization  tends  to  loosen  the  denture. 

Atmospheric  Pressure. — ^As  is  well  known,  atmospheric 
pressure  is  the  weight  of  a  column  of  air  resting  upon  an 
object.    The  weight  of  a  column  of  air  at  the  sea  level  is  14.7 


ATMOSPHERIC  PRESSURE  273 

pounds  to  the  square  inch,  and  decreases  in  ratio  to  the 
height  above  sea  leveh  As  this  pressure  is  equal  in  every 
direction  upon  and  within  the  human  body,  it  is  not  per- 
ceptible. Whenever  a  portion  of  this  column  of  air  is 
removed  from  a  circiunscribed  portion  of  the  body,  its 
effect  is  immediately  felt.  No  substance  can  be  placed 
between  the  atmosphere  and  the  surface,  or  a  portion  of 
the  surface,  of  the  body,  and  remove  the  pressure  of  the 
atmosphere  from  the  body,  as  the  intervening  substance, 
being  contiguous,  would  be  held  against  the  surface  of  the 
body  by  the  full  weight  of  the  column  of  air  resting  upon  it. 
Thus  we  may  justly  conclude  that  an  artificial  denture  per- 
fectly adjusted  to  the  tissues  of  the  mouth  would  be  retained 
by  the  full  weight  of  the  column  of  air,  or  approximately 
fifteen  pounds  for  each  square  inch  of  surface  covered;  also 
that  a  chamber  cut  in  the  maxillary  surface  of  the  plate 
would  be  a  positive  detriment,  because  it  would  be  an  air 
chamber  equalizing  the  column  of  air  upon  the  external 
surface  of  the  plate  to  the  extent  of  the  air  chamber.  How- 
ever, there  is  a  fatal  obstacle  to  this  imaginary  retention  of 
an  artificial  denture,  for  it  is  a  physical  impossibility  to 
exclude  the  film  of  air  between  the  soft  tissues  of  the  mouth 
and  the  hard  base-plate  except  by  substituting  a  fluid  for 
the  film  of  air.  By  the  substitution  of  this  fluid  for  the 
film  of  air  the  law  of  hydrostatics  is  introduced.  The  law 
of  hydrostatics  is,  that  a  pressure  placed  upon  a  confined 
liquid  is  equal  in  every  direction.  Therefore  a  mechanically 
perfectly  adapted  artificial  denture  having  a  fluid  contact 
cannot  be  retained  by  atmospheric  pressure,  because  the 
intervening  fluid  equalizes,  within  and  without,  the  atmos- 
pheric pressure. 

Atmospheric  pressure  may  be  utilized  to  retain  an  artificial 
denture,  but  through  the  medium  only  of  a  vacuum  chamber. 
Since  an  absolute  vacuum  is  an  impossibility,  the  amount 
of  retention  by  atmospheric  pressure  is  contingent  upon 
the  square  surface  of  the  chamber  and  the  vacuity  obtained. 
To  produce  any  degree  of  vacuity  it  is  necessary  to  have  the 
plate  surrounding  the  vacuum  cavity  perfectly  adapted  to 
18 


274  RETENTION  OF  ARTIFICIAL  DENTURES 

the  soft  tissues.  The  extent  of  exhaustion  of  the  air  from 
the  chamber  is  governed  by  the  power  of  the  muscles  of  the 
tongue  and  the  ability  of  the  patient  to  apply  them.  The 
exhaustion  is  produced  by  forceful  swallowing. 

Retention  by  atmospheric  pressure  can  only  be  temporary, 
and  maintained  only  so  long  as  there  is  a  partial  vacuum. 
The  effect  of  the  vacuum  chamber  upon  the  tissues  of  the 
mouth  is  the  same  as  cupping  in  medical  practice.  As  soon 
as  the  atmospheric  pressure  is  reduced  upon  a  circum- 
scribed portion  of  the  body,  it  acts  as  an  excitant,  causing  an 
increased  blood  pressure  in  the  part,  with  a  temporary 
swelling,  and  if  continued  a  proliferation  of  tissue  cells, 
producing  a  permanent  growth  until  the  chamber  is  filled. 
When  the  chamber  is  filled  by  tissue  and  the  fluids  of  the 
mouth,  atmospheric  pressure  can  no  longer  exist;  the  denture 
is  then  retained  only  by  adhesion  by  contact.  While  the 
term  "suction  plate"  is  not  so  euphonious  as  "atmospheric 
pressure  plate,"  it  more  nearly  expresses  the  truth  without 
attempting  an  explanation  of  how  the  suction  is  secured. 

As  the  amount  of  retention  of  a  vacuum  chamber  stands 
in  direct  ratio  to  its  square  surface,  so  its  relative  permanence 
and  its  injurious  effects  stand  in  direct  ratio  to  its  depth. 

Adhesion  by  Contact. — This  retentive  force  is  often  confused 
with  atmospheric  pressure,  whereas  it  is  an  entirely  differ- 
ent principle.  Atmospheric  pressure  retention  is  contingent 
upon  a  chamber  which  is  more  or  less  evacuated  of  air,  while 
adhesion  by  contact  is  conditioned  by  uniform  pressure 
and  absolute  contact.  To  comprehend  this  principle  of 
retention,  the  molecular  forces  of  attraction  and  repulsion 
must  be  appreciated.  These  two  molecular  forces,  to  a 
greater  or  less  extent,  exist  within  and  between  all  bodies. 
In  solid  matter  attraction  predominates  over  repulsion, 
whereas  in  liquids  the  two  forces  are  equal,  and  in  gaseous 
matter  repulsion  predominates  over  attraction.  Attraction 
is  always  stronger  between  like  atoms  than  between  unlike 
atoms.  (This  last  fact  is  beautifully  illustrated  in  the 
low-fusing  alloys  composed  of  tin,  lead,  bismuth,  and 
cadmium.    These  metals  range  in  fusing  point  from  442°  F. 


LEVERAGE  275 

to  617°  F.,  yet  when  they  are  properly  combined  they  may 
fuse  at  135°  F.,  thus  demonstrating  that  the  molecules  of 
these  metals  create  a  marked  repulsion  for  each  other,  and 
that  it  takes  but  a  low  degree  of  heat  to  render  attraction  and 
repulsion  equal,  that  is,  for  the  metals  to  fuse  to  a  liquid 
state.)  When  like  atoms  are  brought  into  atomic  relation 
to  each  other,  they  are  said  to  be  held  together  by  cohesion; 
when  the  interatomic  space  is  exceeded,  they  can  only  be 
held  together  by  adhesion,  either  by  mass  attraction  or  an 
intervening  adhesive  substance.  Thus,  it  is  apparent  that 
the  expression  "uniform  pressure"  and  "absolute  contact" 
are  misnomers,  because  absolute  contact  is  an  impossibility; 
but  when  these  terms  are  used,  they  signify  the  closest 
mechanical  contact  of  the  mass,  and  do  not  refer  to  the  atom 
relationships.  When  masses  of  matter  are  brought  into 
mechanical  contact  and  are  caused  to  adhere  by  a  film  of 
non-adhesive  fluid,  it  might  be  thought  that  the  adhesion  is 
due  to  the  strength  of  the  fluid;  but  this  is  not  the  case, 
because  the  thinner  the  film  the  greater  the  adhesion.  That 
this  adhesion  is  not  due  to  atmospheric  pressure  may  be 
demonstrated  by  suspending  two  masses  of  matter  adhering 
by  contact  in  the  chamber  of  an  air  pump  and  exhausting  the 
air,  when  the  adhesion  will  remain  the  same  or  stronger  than 
under  normal  atmospheric  conditions.  Therefore,  through 
an  understanding  of  these  axioms  regarding  attraction  and 
repulsion,  we  can  appreciate  how  artificial  dentures  are 
retained  by  the  so-called  adhesion  by  contact. 

Leverage. — In  mechanics  the  lever  is  a  rigid  bar  working 
upon  a  pivot.  The  pivot  is  called  the  fulcrum,  and  the  bar  is 
considered  as  two  portions  called  arms,  the  one  called  the 
power  arm  and  the  other  the  work  arm.  There  are  three 
groups  of  these  factors — fulcrum,  power  and  work  arms — 
called  classes.  In  the  first  class  the  fulcrum  is  between  the 
power  and  the  work,  whereas  in  the  second  class  the  work  is 
between  the  fulcrum  and  the  power;  in  the  third  class  the 
power  is  between  the  fulcrum  and  the  work.  In  the  retention 
of  artificial  dentures  the  lever  of  the  first  class  only  neerl  be 
considered,  and  it  is  of  great  importance.     This  principle 


276  RETENTION  OF  ARTIFICIAL  DENTURES 

of  physics  is  involved  in  every  case  of  prosthetic  restoration, 
either  in  its  positive  or  negative  sense,  and  too  often  in  both. 
In  complete  artificial  dentures  the  alveolar  ridge  constitutes 
the  fulcrum,  and  the  retention  of  the  base-plate,  by  either 
atmospheric  pressure  or  adhesion  by  contact,  constitutes  the 
power;  the  portion  of  the  base-plate  upon  which  these  reten- 
tive forces  exert  their  influence  constitutes  the  power  arm. 
The  teeth  form  the  work  arm,  and  antagonization  is  the  work. 
In  partial  artificial  dentures  the  remaining  natural  teeth  and 
roots  may  be  the  fulcrum  or  even  fulcrums. 

The  law  governing  the  direction  of  energy  should  be  taken 
into  consideration.  The  law  is :  Energy  moves  in  a  straight 
line  and  at  right  angles  to  the  surface  from  which  the  force 
emanates.  Thus,  in  the  line  of  energy  there  may  be  great 
resistance,  while  laterally  there  would  be  but  slight  resistance. 
(This  is  well  illustrated  by  two  plates  of  glass  held  together 
by  adhesion  by  contact,  which  will  offer  much  resistance  to 
an  effort  to  pull  them  directly  apart,  but  only  slight  resist- 
ance to  lateral  pressure.) 

The  anatomical  relation  of  the  mandible  to  the  maxillae 
is  a  peculiar  one,  and  offers  many  problems  in  physics.  As 
resorption  of  the  alveoli  progresses,  these  adverse  con- 
ditions become  exaggerated.  Therefore  it  follows  that 
artificial  substitutes  should  be  inserted  soon,  that  is,  within 
a  few  weeks — two  to  six — after  the  removal  of  the  natural 
teeth.  As  the  resorption  of  the  alveolar  processes  progresses, 
the  summit  of  the  alveolar  ridge  of  the  upper  jaw  recedes 
upward  and  inward,  whereas  the  summit  of  the  alveolar 
ridge  of  the  mandible  recedes  downward  and  outward. 
Hence,  if  the  artificial  teeth  are  set  in  the  position  occupied 
by  the  natural  teeth,  the  problems  in  leverage  become  very 
serious.  It  is  apparent  that  if  the  upper  teeth  could  be 
arranged  with  their  buccal  surfaces  just  inside  the  summit 
of  the  alveolar  ridge,  it  would  be  impossible  to  dislodge 
the  base-plate  by  direct  occlusion,  no  matter  how  hard  or 
circumscribed  the  bolus  of  food;  but  it  is  not  practical  to  so 
arrange  the  teeth;  it  is  desirable,  from  a  mechanical  point  of 
view,  to  approach  this  condition  as  nearly  as  the  individual 


RETENTION  OF  FULL  ARTIFICIAL  DENTURES     277 

case  will  permit.  If  after  the  alveoli  have  thoroughly 
receded  the  upper  artificial  teeth  are  mounted  upon  the  base- 
plate in  their  normal  distance  from  the  raphe,  the  work 
arm  of  the  lever  is  relatively  much  lengthened.  Therefore, 
to  overcome  this  untoward  leverage  the  teeth  are  drawn 
in  toward  the  summit  of  the  ridge.  There  is  a  limit  to  the 
inward  drawing  of  the  lingual  surface  of  the  teeth,  for  undue 
encroaching  upon  the  domain  of  the  tongue  will  ensue.  That 
this  work  arm  may  be  still  further  shortened,  the  artificial 
teeth  buccolingually  are  made  narrower  than  normal.  As 
the  shortening  of  a  radius  shortens  the  circimiference  of  a 
circle,  it  becomes  necessary  to  select  artificial  bicuspids  and 
molars  a  little  narrower  mesiodistally  than  the  natural  teeth 
which  they  replace.  This  is  but  one  of  the  reasons  for  the 
reduced  size  of  the  grinding  teeth.  The  other  reason  for 
reducing  the  size  of  these  teeth  has  to  do  with  their  power, 
and  should  not  be  discussed  together  with  the  principles 
of  retention.  It  has  already  been  stated  that  motion — 
force — moves  at  right  angles  to  the  surface  from  which  the 
motion  emanates,  therefore  the  shaping  of  the  facets  of  the 
occlusal  surface  of  the  bicuspids  and  molars  is  an  important 
factor  in  the  problem  of  leverage. 


CONDITIONS  AFFECTING  RETENTION  OF  FULL 
ARTIFICIAL  DENTURES 

There  are  four  factors  to  be  considered  in  the  retention 
of  base-plates:  Size,  that  is,  the  amount  of  surface  covered; 
soft  tissue;  fluids  of  the  mouth;  and  the  shape  of  the  portion 
covered. 

Size. — In  any  given  case  the  amount  of  retention  by 
adhesion  by  contact  is,  like  atmospheric  pressure,  according 
to  the  area  of  the  surface  (P'ig.  104.)  Hence,  other  things 
being  ecjual,  the  larger  the  denture  the  better  the  retention. 

Soft  Tissue.  No  one  factor  has  so  much  to  do  with 
retentifju  of  artificial  dentures  as  the  soft  tissues.  These 
may  be  divided  into  three  classes — muscles  and  their  attach- 


278 


RETENTION  OF  ARTIFICIAL  DENTURES 


merits,  submucous  tissue,  and  the  mucous  membrane.  As 
an  axiom,  it  may  be  stated  that  a  base-plate  cannot  rest 
upon  a  muscle  which  impinges  upon  or  draws  over  the 
periphery  of  the  plate,  as  the  contractile  power  of  the  muscle 
is  greater  than  the  retentive  force  of  adhesion  by  contact; 
also  of  atmospheric  pressure.  The  muscle  attachments 
should  always  be  observed  in  examining  the  mouth  prior  to 
taking  the  impression;  then,  in  taking  the  impression,  the 
muscles  should  be  marked  in  the  impression,  so  that  the 


base-plate  may  secure  a  close  adaptation  about  the  muscle 
attachments,  and  yet  not  be  dislodged  thereby.  As  adhesion 
by  contact  is  in  the  ratio  to  the  surface  covered,  it  is  apparent 
that  the  base-plate  should  extend  as  far  in  every  direction 
as  the  attachment  of  the  muscles  will  permit,  but  not  so 
far  that  the  muscles  when  placed  upon  their  greatest  tension 
will  impinge  upon  the  periphery  of  the  base-plate  suffi- 
ciently to  dislodge  it.  This  may  give  a  very  irregular  outline, 
but  the  proper  outlining  of  the  periphery  of  the  base-plate 
is  one  of  the  important  operations  in  adapting  artificial 


RETENTION  OF  FULL  ARTIFICIAL  DENTURES     270 

dentures.  Beginning  in  the  median  line,  the  labial  flange 
of  the  upper  base-plate  should  be  well  cut  away  for  the 
labial  frenum,  then  gradually  ascend  to  the  cuspid  eminence, 
where  for  cosmetic  effects  it  must  be  as  high  as  possible. 
After  forming  the  outline  of  the  cuspid  eminence,  the  border 
of  the  flange  abruptly  drops  to  accommodate  the  buccal 
frenum.  The  remainder  of  the  border  to  the  tuberosity  must 
be  kept  as  high  as  the  attachment  of  the  buccinator  muscle 
will  permit.  In  passing  around  the  tuberosity,  if  there  be 
one,  the  edge  of  the  base-plate  must  not  impinge  too  much 
upon  the  soft  tissues.  After  trimming  the  base-plate  to 
what  seems  to  be  the  proper  outline,  it  should  be  tested  by 
moistening  the  maxillary  surface,  placing  it  in  the  mouth, 
and  instructing  the  patient  how  to  exhaust  the  air  from 
between  the  base-plate  and  the  soft  tissues  upon  which  it 
rests.  The  patient  should  then  be  requested  to  vigorously 
work  the  muscles  of  the  lip  and  cheeks,  and  see  if  in  any 
way  the  base-plate  may  be  dislodged.  If  so,  the  patient 
should  again  attach  the  base-plate,  the  operator  grasping  the 
lip  and  cheeks,  one  portion  at  a  time,  between  the  thumb 
and  finger,  and  firmly  extend  the  tissues  outward  and  down- 
ward until  the  point  or  points  that  are  not  properly  relieved 
are  discovered. 

The  lower  base-plate  is  of  the  horseshoe  or  crescent  shape, 
and  necessarily  covers  much  less  surf  ace  than  the  upper  one; 
but  if  the  impression  is  properly  taken  and  the  periphery 
properly  adjusted  for  the  muscle  attachments,  the  base- 
plate can  be  seated,  and  sometimes  considerable  adhesion 
obtained.  Some  writers  would  lead  one  to  believe  that 
all  lower  artificial  dentures  should  have  a  deep  lingual 
flange,  while  other  writers  would  have  the  lingual  flange 
almost  entirely  removed.  Both  are  correct,  because  some 
cases  require  the  one  treatment  and  other  cases  the  other 
method.  In  those  cases  in  which  the  crest  of  the  alveolar 
process  of  the  mandible  is  pronounced,  and  the  attachment 
of  the  mylohyoid  muscle  is  low  upon  the  lingual  wall,  the 
lingual  flange  of  the  base-plate  can  and  should  be  carried 
well  down,  for  adhesion  by  contact  is  according  to  the  area 


280  RETENTION  OF  ARTIFICIAL  DENTURES 

of  the  surface,  and  the  larger  the  base-plate  the  greater 
the  resistance  to  the  force  of  mastication;  but  if  there  is 
excessive  resorption  of  the  process,  and  the  attachment  of 
the  mylohyoid  is  at  or  very  near  the  crest  of  the  slight  ridge 
remaining,  or  if  there  is  a  sharp  edge  representing  the  union 
of  the  lingual  plate  of  the  mandible  and  the  remains  of  the 
alveolar  process,  there  should  be  almost  no  lingual  flange 
to  the  base-plate.  If  in  taking  the  impression  the  mylo- 
hyoid is  compressed  and  depressed,  the  apparent  space  for  a 
lingual  flange  will  prove  very  delusive  and  troublesome; 
also,  if  the  base-plate  is  carried  over  the  sharp  lingual  edge 
often  found  upon  the  mandible,  much  irritation  will  be 
produced.  In  these  cases  the  only  means  of  success  is  to 
cut  away  the  lingual  flange,  if  one  has  been  formed.  In 
constructing  the  superstructure  upon  this  properly  fitted 
short  lingual  flanged  base-plate,  an  extra  retention  flange 
of  one-sixteenth  to  three-sixteenths  of  an  inch  in  width  may 
be  extended  horizontally  into  the  mouth,  when  the  glands 
and  folds  of  mucous  membranes  resting  upon  this  enlarged 
base-plate  will  often  be  of  much  aid  in  retention.  The  buccal 
flange  should  be  kept  as  broad  as  the  muscle  attachments 
will  permit.  The  same  tests  applied  to  the  upper  base- 
plates should  be  used  with  the  lower. 

Submucous  Tissue. — In  this  class  is  included  all  the  soft 
tissue  of  whatever  histological  formation — except  the  muscle 
tissue  just  considered — lying  beneath  the  mucous  membrane 
upon  which  the  base-plate  rests.  When  a  moderate  amount 
of  soft  tissue  is  evenly  disposed  beneath  the  mucous  mem- 
brane, the  very  best  condition  possible  so  far  as  this  tissue 
is  concerned  is  presented.  In  some  mouths  the  raphe  of  the 
maxillse  will  be  found  overdeveloped  and  covered  with  a 
thin,  tensely  drawn  mucous  membrane,  while  upon  either 
side  there  may  be  an  area  extending  well  toward  the  base  of 
the  alveolar  process  with  more  or  less  submucous  tissue,  and 
a  portion  of  the  alveolar  ridge  composed  of  soft  flabby  tissue 
only.  If  an  aged  patient  presenting  such  a  mouth  has  not 
long  since  acquired  the  knack  of  wearing  artificial  dentures, 
the  chances  of  his  success  are  very  unfavorable.    The  treat- 


RETENTION  OF  FULL  ARTIFICIAL  DENTURES     281 

ment  for  such  a  case  would  be  to  relieve  the  pressure  upon 
the  whole  length  of  the  raphe,  let  the  soft  tissue  in  the  vault 
alone,  and  increase  the  pressure  upon  the  soft  portion  of  the 
alveolar  ridge.  A  vacuum  chamber  in  such  a  case,  placed 
over  a  portion  of  the  tense  membrane  in  the  highest 
portion  of  the  \ault,  would  be  a  source  of  irritation  and 
useless. 

Mucous  Membrane. — This  membrane  must  bear  the  burden 
of  supporting  all  complete  artificial  dentures,  therefore  an 
appreciation  of  its  capabilities  is  an  important  factor  to  the 
prosthetist.  In  examining  the  mouth  prior  to  taking  the 
impression  the  condition  of  health  of  this  tissue  over  which 
the  base-plate  is  to  be  placed  should  be  noted,  and  if  neces- 
sary, the  required  attention  given.  There  are  two  qualities 
of  this  membrane  to  be  considered,  tone  and  tension. 

Tone. — This  membrane  is  much  influenced  by  the  health 
of  the  individual,  and  may  be  quite  an  index  of  the  condition 
of  the  general  system.  The  patient  will  learn  that  when  the 
general  system  is  vigorous  and  rested,  the  denture  will  have 
its  maximum  retention,  but  when  the  system  is  debilitated  or 
relaxed  from  temporary  exhaustion — tired — the  retention  of 
the  denture  will  be  poor  and  troublesome.  When  patients 
complain  that  their  dentures  are  not  "sticking  up"  as  well 
as  they  did,  it  is  well  to  investigate  the  tone  of  the  system 
and  explain  this  principle.  When  the  mucous  membrane 
loses  tone  for  any  reason,  the  retention  of  the  denture  will 
be  correspondingly  aflected.  When  dissolution  is  about  to 
take  place,  it  may  be  noticed  that  artificial  dentures  cannot 
be  retained  at  all.  Because  of  this  quality  of  tone,  other 
conditions  being  equal,  the  younger  the  patient  the  better 
the  retention.  Aged  patients  in  a  debilitated  state  of  health 
and  unacquainted  with  the  use  of  artificial  dentures  should 
not  be  encouraged  in  having  their  mouths  fitted  to  new 
dentures,  for  the  tax  upon  their  vitality  may  be  too  great, 
and  hasten  their  death. 

Tension. — When  a  surface  upon  which  a  denture  is  to  be 
worn  is  covered  with  a  healthy  mucous  membrane,  evenly 
underlaid  with  a  medium  amount  of  submucous  tissue,  and 


282  RETENTION  OF  ARTIFICIAL  DENTURES 

the  tone  is  good,  so  far  as  the  tissues  are  concerned,  the 
very  best  conditions  exist  for  retaining  an  artificial  denture. 

When  the  soft  tissues  covering  the  roof  of  the  mouth  are 
thin  and  tense,  the  case  is  much  more  difficult.  In  the  former 
case  the  tissues  will  quickly  conform  to  the  hard  base-plate, 
and  if  there  has  been  a  reasonably  skilful  construction  of  the 
appliance,  the  retention  will  be  satisfactory.  In  the  latter 
case,  with  the  most  skilful  construction,  it  will  often  require 
an  hour  or  two  before  the  mucous  membrane  conforms  to  the 
unyielding  material  of  the  base-plate.  It  is  this  class  of  cases 
that  tempt  the  dentist  to  use  velum  vulcanite  lining  at  the 
periphery  of  the  base-plate,  or  to  resort  to  the  patent  soft 
vulcanite  retainers.  As  this  condition  of  the  mouth  is  the 
only  logical  one  in  which  these  retainers  are  permissible, 
little  harm  is  done  if  they  are  never  used  where  not  indicated. 
In  these  cases  of  tense  mucous  tissue  no  sharp  edges  or 
localized  increased  pressure  by  any  means  whatever  can  be 
tolerated.    Carving  of  the  cast  is  contraindicated. 

When  the  mucous  membrane  is  extensively  underlaid  with 
soft  tissue  over  the  roof  of  the  mouth,  and  deeply  fissured, 
the  case  may  justly  be  classed  as  unfavorable  for  retention. 
The  cast  of  such  a  case  may  be  carved  with  impunity.  The 
object  sought  in  carving  is  to  cause  the  periphery  of  the  plate 
to  embed  itself  more  firmly,  or  to  raise  a  bead  just  inside  of 
the  periphery.  This  temporarily  creates  a  large  vacuum 
chamber,  but  as  soon  as  the  raised  portion  becomes  embedded 
in  the  soft  tissues,  adhesion  by  contact  is  secured.  In  some 
cases  the  bead  acts  as  a  barrier  to  the  ingress  of  an  excessive 
amount  of  fluid. 

Many  cases  presenting  will  have  areas  of  thin,  tense 
tissue,  and  other  areas  of  excessively  soft  tissue.  The  treat- 
ment for  this  class  of  cases  has  already  been  stated,  that  is, 
relieving  of  the  pressure  upon  the  tense  tissue  in  the  prox- 
imity of  the  raphe,  to  the  extent  of  its  entire  length.  This 
can  usually  be  accomplished  by  the  addition  of  one  or  two 
layers  of  No.  60  tinfoil.  The  soft  areas  over  any  portion  of 
the  vault  should  not  be  changed,  but  an  excessively  soft 
tissue  upon  the  alveolar  ridge  should  be  compressed-    Rarely 


THE  PRINCIPLES  OF  RETENTION  283 

should  any  hard  portion  of  the  alveolar  ridge  be  relieved, 
and  then  only  when  very  circumscribed. 

Fluids  of  the  Mouth. — The  normal  thin  watery  fluid  of  the 
mouth  is  most  favorable  for  retention  by  adhesion  by 
contact.  The  fluid  makes  the  contact,  but  does  not  hold 
the  base-plate  so  far  away  as  to  interfere  with  the  adhesion 
by  contact.  When  the  fluids  are  vitiated,  thick,  and  ropy, 
they  may  have  sticky  properties,  but  not  enough  to  com- 
pensate for  the  interference  with  adhesion  by  contact. 
Temporarily  these  vitiated  secretions  can  be  removed  from 
the  mouth  by  thoroughly  washing  with  an  alkaline  solution, 
then  inserting  the  denture  well  moistened  with  cold  water. 

Shape. — The  shape  of  the  siu'face  upon  which  an  artificial 
denture  is  to  rest  has  much  to  do  with  its  retention.  Side 
walls  are  useful  to  prevent  lateral  motion;  but  a  flat  surface 
in  the  vault,  or  floor  of  the  mouth,  is  essential  for  suction. 
No  matter  whether  the  vault  is  high  or  low,  or  the  alveolar 
process  of  the  mandible  is  high  or  low,  the  retentive  surface 
is  the  horizontal  surface  presenting.  A  high  inverted  V- 
shaped  vault  or  alveolar  process  of  the  mandible  is  especially 
unfavorable  for  suction. 


PRACTICAL  APPLICATION  OF  THE  PRINCIPLES  OF 
RETENTION 

The  retention  of  full  dentures  may  be  said  to  be  by  four 
forces:  two  passive — first,  base-plate  outline,  and  second, 
resistance  to  force  (leverage) — and  two  active — first,  molec- 
ular (adhesion  by  contact),  and  second,  atmospheric  pressure 

Base-plate  Outline. — Much  of  the  burden  of  the  discussion 
in  Chai)ter  I  is  developing  the  anatomy  of  the  mouth  as  a 
support  for  and  retention  of  artificial  dentures;  therefore,  the 
chapter  may  again  be  read  with  this  subject,  "base-plate 
outline  and  retention,"  uppermost  in  mind.  Figs.  00  and 
()1  illustrate  outlines  for  a  s[)ecific  ui)per  and  lower  case. 
If  the  impressions  are  properly  taken  the  landmarks  are 
defined. 


284 


RETENTION  OF  ARTIFICIAL  DENTURES 


Leverage. — Figs.  165  and  166  illustrate  the  application 
of  force  through  the  teeth  upon  the  base-plate.  Where 
there  are  two  facets,  as  in  the  bicuspids,  the  force  may  be 
applied  from  either  facet,  then  the  direction  of  the  force  will 
be  at  right  angle  to  that  surface;  but  if  the  force  is  applied 
to  both  surfaces,  the  direction  of  the  force  will  be  the  result- 
ant, and  parallel  with  the  long  axis  of  the  tooth  or  teeth. 
Each  specific  case  should  be  carefully  studied,  and  these  two 
factors,  outline  and  leverage,  should  be  so  controlled  that 
they  aid  in  retention  and  not  in  dislodging  the  artificial 
dentures.  These  factors  are  classed  as  passive  forces,  because 
it  is  through  them  that  active  muscular  force  may  cause 


Fig.   165 


Fig.   16C 


destructive  motion.  Fig.  167  illustrates  a  practical  case 
in  which  success  was  not  attained  until  the  tilted  molar 
on  each  side  of  the  mandible  was  cut  down  and  crowned. 

Molecular  Attraction,  or  Adhesion  by  Contact. — Adhesion  by 
contact  is  described  by  the  catchy  phrase,  "  uniform  pressure 
and  absolute  contact,"  while,  in  fact,  neither  statement  is  true. 
What  is  meant  is,  that  the  base-plate  is  so  adjusted  that  it 
resists  force  applied  at  any  point  within  the  base  plane.  In 
practice  this  means  that  the  heaviest  bearing  of  the  base- 
plate is  at  and  near  the  periphery.  Absolute  contact  means 
that  there  are  no  cavities  made  in  the  surface  of  the  denture 
as  suction  chambers;  but  it  does  admit  of  and  requires  relief 
of  enclosed  hard  places.     These  relief  spaces  undoubtedly 


THE  PRINCIPLES  OF  RETENTION 


285 


do  cause  temporary  suction,  but  this  is  incidental  and  not 
the  object.     The  shape  of  these  rehef  spaces  are  usually 


Fig.   167 


different  from  that  of  vacuum  chambers.     They  conform  to 
the  shape  of  the  hard  portion  to  be  relieved,  while  the 


286 


RETENTION  OF  ARTIFICIAL  DENTURES 


vacuum  chamber  is  in  miniature  the  outhne  of  the  alveolar 
process.  The  most  commonly  required  relief  is  along  the 
raphe  of  the  maxillae  (Fig.  168).  This  relief  may  be  made 
by  adding  one  or  more  thicknesses  of  number  60  S.  S.  W. 
tinfoil.  This  foil  is  4|  thousandths  of  an  inch  thick,  hence 
the  desired  depth  of  the  relief  space  may  be  obtained  by 
additional  layers  of  foil.  The  relief  should  be  over  the  whole 
length  of  the  hard  portion,  even  though  it  extend  from  the 
crest  of  the  alveolus  to  (and  even. through)  the  palatal  border 


Fig.    169 


Wg} 

^M 

Wm 

1 

1 

//      ^^1 

L    ^ 

— TV 

H 

of  the  base-plate.  Fig.  169  represents  three  layers  of  relief 
tin.  The  first,  the  smallest  one,  is  fastened  to  the  plaster 
cast  with  sandarac  varnish,  the  second  one  in  size  is  glued 
over  the  first,  and  the  third  and  largest  is  fastened  in  like 
manner.  Any  circumscribed  hardness,  as  nodules,  wherever 
located,  should  be  relieved  in  the  same  manner  as  described 
for  the  raphe.  Another  method  for  relieving  the  hard 
places  is  by  compressing  the  soft  places.  This  should  be 
done  by  the  manner  in  which  the  impression  is  taken  which 
is  discussed  in  Chapter  11.    In  few  cases  is  it  advisable  to 


THE  PRINCIPLES  OF  RETENTION  287 

carve  the  impression  or  cast  to  produce  this  rehef,  as  the 
amount  removed  cannot  be  correctly  gauged,  nor  the  original 
condition  restored  if  desirable. 

Atmospheric  Pressure. — Since  its  application  to  artificial 
dentures,  in  1840,  there  has  been  and  is  much  confusion  of 
thought  and  expression  over  the  theory  and  practice  M^ith 
this  physical  force.  The  student,  after  giving  consideration 
to  the  truths  stated  in  the  preceding  sections  of  this  chapter, 
should  ha\e  no  difficulty  in  formulating  a  terse  statement,  for 
memory  purposes,  as :  Molecular  attraction,  mass  attraction, 
or  adhesion  by  contact  (used  as  synonymous  terms)  implies 
mechanical  contact;  and  atmospheric  pressure  implies  a 
space  with  some  degree  of  emptiness. 

It  is  evident  that  the  most  advantageous  position  for  a 
vacuum  chamber  is  about  the  gravity  centre  of  the  denture, 
which  has  the  least  motion,  and  where  the  leverage  is  equal 
in  every  direction.  The  following  demonstration  and 
application  is  from  Dr.  Burchard  in  the  American  Text-book 
of  Prosthetir  Dentistry: 

"The  slight  movement  usual  with  a  plate  during  masti- 
cation tends  to  separate  it  from  the  mucous  membrane  and 
permit  the  access  of  air  to  its  under  surface. 

"The  line  of  least  movement,  as  the  movement  is  lateral, 
a  rocking  from  side  to  side,  is  along  the  median  line  of  the 
vault;  and  as  the  concavity  of  the  hard  palate  is  usually  of 
an  irregular  vault  form,  the  point  of  least  movement  is  near 
its  apex.  If  the  movement  does  not  extend  to  an  edge  of  the 
chamber,  the  stability  of  the  plate  is  not  materially  afl'ected, 
but  when  one  of  these  edges  loses  its  contact,  air  enters  the 
chamber  and  adhesion  is  destroyed. 

"The  more  closely  the  edges  of  the  chamber  approximate 
this  line  the  less  tendency  to  disturbance  there  is,  so  that  com- 
paratively narrow  chambers  are  to  be  preferred;  but  the 
depression  should  be  of  sufficient  size  to  not  materially  lessen 
the  effect  of  a  partial  vacuum.  Naturally  the  chamber 
should  be  in  the  area  of  greatest  stability,  that  of  least 
movement.     This  area  will  be  found  around  and  about  the 


288 


RETENTION  OF  ARTIFICIAL  DENTURES 


centre  of  gravity,  and  in  shape  resembling  the  outhnes  of  the 
dental  arch. 

"The  dental  arch  represents,  approximately,  a  parabola 
in  outHne.     This  encloses  a  trapezoid,  the  centre  of  the 


Fig.   17(1 

D/v                                   1                                   /\^ 

/     y ''"'    1  ^\  ^  \      \ 

Fig.   171 


cuspids  marking  the  extremities  of  the  short,  the  centres  of 
the  third  molars  those  of  the  long,  parallel  side.  Straight 
lines  joining  these  points  complete  the  figure.  The  centre 
of  gravity  of  a  trapezoid  is  found  by  suspending  it  first 
by  one  obtuse  angle  and  next  by  one  of  the  acute  angles; 


THE  PRINCIPLES  OF  RETENTION  289 

vertical  lines  dropped  from  the  points  of  suspension  will, 
in  intersecting,  mark  the  centre  of  gravity.  Thus,  on  the 
diagram  (Fig.  170,  ABC  D)  suspend  it  first  from  the 
angle  ADC  and  drop  a  vertical,  D  F.  Suspend  from  the 
angle  BAD  and  drop  a  vertical,  A  E.  Their  intersection  at 
the  point  G  is  the  centre  of  gravity,  which  is  posterior  to 
the  intersection  of  the  diagonals."  In  Fig.  171  application 
of  the  principal  is  applied  to  the  cast. 

"  About  the  centre  of  gravity  the  vacuum  chamber  should 
be  placed,  its  outline  following  that  of  the  arch,  on  a  smaller 
•scale.  In  the  vast  majority  of  cases  the  centre  of  gravity 
thus  determined  will  be  found  at  about  the  height  of  the 
vault. 

"The  ends  or  apex  and  angles  of  the  chamber  should  be 
about  equidistant  from  the  centre  of  gravity — as  a  rule, 
the  apex  of  the  chamber  as  far  in  front  of  the  intersection  of 
the  diagonals  as  the  centre  of  gravity  is  behind  that  point. 

"To  apply  these  facts  practically  as  a  guide  to  finding 
the  correct  position  of  a  chamber,  draw  first  on  the  plaster 
cast  the  median  line  of  the  vault.  From  the  centres  of  the 
cuspids  to  the  centres  of  the  third  molars  draw  diagonal 
lines,  the  diagonals  of  the  trapezoid.  When  all  the  teeth  are 
absent,  draw  the  two  diagonals  from  the  position  formerly 
occupied  by  the  cuspids  to  the  centres  of  the  tuberosities. 

"To  find  the  centre  of  gravity,  draw  from  the  centres  of 
both  tuberosities  lines  to  the  junction  of  the  first  and  second 
bicuspids  of  the  opposite  sides  other  lines,  which  intersect 
at  a  point  of  the  median  line  G;  this  point  will  be  the  centre 
of  gravity  of  the  trapezoid  and  of  the  palatal  vault.  The 
intersection  of  the  diagonals  will  mark  the  focus  of  the  small 
parabolic  area  to  be  covered  by  the  chamber  piece.  Draw 
this  parabola,  its  apex  about  as  far  in  front  of  the  point  of 
intersection  of  the  diagonals  as  the  centre  of  gravity  is 
behind  the  latter  point,  the  angle  of  the  parabola  the  same 
clistance  from  the  centre  of  gravity  as  the  apex.  Should 
there  be  a  lack  of  harmony,  of  bilateral  symmetry  of  the 
right  or  left  side  of  the  arch  outline,  make  the  outlines  of 
the  chamber  in  correspondence." 
19 


290  RETENTION  OF  ARTIFICIAL  DENTURES 


CONSTRUCTING  VACUUM  CHAMBERS 

Edges. — The  edges  of  relief  spaces  should  be  almost 
imperceptible,  while  the  edges  of  a  vacuum  space  should  be 
at  right  angle  to  the  contact  surface.  The  depth  of  the 
vacuum  cavity  should  vary  from  -^-^  to  y  g-  of  an  inch.  The 
thinner  and  tenser  the  tissue  the  shallower  the  chamber,  and 
vice  versa. 

Material. — Block  tin  or  tin  alloyed  with  lead  is  used  to 
form  the  vacuum  chamber.  Pure  lead  may  be  used,  but  it 
imparts  a  dark  discoloration  to  the  vulcanite.  The  pattern 
metal  found  at  the  supply  houses  is  tin  with  a  small  amount 
of  lead.  The  material  should  be  purchased  in  the  sheet 
form  and  cut  for  each  case.  As  the  metal  is  supplied  in 
sheet  form  yg^  of  an  inch  thick,  a  small  portion  should  be 
rolled  to  3^  of  an  inch  and  the  larger  portion  to  g^y  of  an 
inch  in  thickness.  All  fanciful  forms  having  sharp  angles 
(as  heart  or  shield  shape)  should  be  avoided  because  they  are 
an  unnecessary  source  of  irritation. 

Attaching. — There  are  various  ways  of  attaching  the 
chamber  forms  to  the  cast,  as  a  thin  mix  of  oxyphosphate  of 
zinc  cement  (best),  sandarac  varnish,  very  small  tacks,  or 
a  short  portion  of  pins.  Fig.  172  shows  a  cast  with  a  vacuum 
chamber  form  attached  with  pins.  When  the  cast  is  to  be 
coated  with  tinfoil  the  varnish  and  foil  will  suffice  to  hold 
the  chamber  form. 

For  Castings. — The  methods  described  for  forming  relief 
spaces  and  vacuum  chambers  are  suitable  for  all  methods  of 
base-plate  formation  excepting  those  by  the  casting  method; 
for  which,  owing  to  the  high  heat  required,  these  methods 
cannot  be  employed.  For  the  casting  method  the  relief 
spaces  and  vacuum  chamber  may  be  provided  for  by  carving 
from  the  impression,  or,  better,  by  adding  to  the  surface  of  the 
cast  a  fine-grain  investment  compound.  This  addition  is 
made  by  tracing,  with  a  pointed  instrument  or  sharp-pointed 
lead  pencil,  the  outline  of  the  desired  addition,  thoroughly 
saturating  the  surface  to  be  added  to  with  water,  and  painting 


CONSTRUCTING  VACUUM  CHAMBERS 


291 


on  the  material  as  a  thin  mix.  A  mixture  of  two  parts,  by 
measure,  of  wash  siHca,  one  part  plaster  of  Paris,  and  water 
to  make  a  thin  cream  is  excellent.  When  the  added  material 
is  nearly  hard  set  it  is  carved  and  burnished  into  form. 

Other  Forms  of  Vacuum  Chambers. — The  vacuum  chamber 
thus  far  considered  and  commonly  used  is  known  as  the 
unilateral  chamber;  that  is,  it  is  one  and  extends  equally 
on  both  sides  of  the  median  line.  There  are  cases  in  which 
this  form  of  chamber  is  not  applicable,  as  cleft  palate,  deep 
fissured  palate,  an  inverted  V  palate,  also  an  overdeveloped 
raphe.     Fig.    173   illustrates  an  overdeveloped  raphe.     In 

Fig.    172 


such  cases  a  bilateral  chamber  is  indicated  if  any  is  to  be 
used.  A  bilateral  chamber  consists  of  a  complete  chamber 
upon  each  side  of  the  median  line.  Fig.  174  is  an  illustration 
of  a  case  requiring  such  treatment. 

Soft  Vulcanite. — The  use  of  "velum  rubber"  (soft  vul- 
canite) retainers  is  a  questionable  method.  It  is  certainly 
unsanitary  and  rarely  justifiable.  There  are  two  general 
plans  for  using  velum  rubber:  (1)  As  a  peripheral  border 
of  the  vacuum  chamber,  or  the  outer  edge  of  the  plate; 
(2j  In  the  form  of  disks,  either  as  a  large  central  disk,  or  as 
small  disks  distributed  about  the  surface.    The  rationale  of 


292 


RETENTION  OF  ARTIFICIAL  DENTURES 


the  first  method  is  to  provide  a  flexible  rim  that  may  be 
readily  adapted  to  a  thin  tense  mucous  membrane.    In  such 


Fig.   173 

'   '^' ., 

X    ■: 

..-^Ji^'%1. 

■\  ■ 

3     % 

^ 

t^'' 

ys 

idife    .„ .,     -  ^ 

■■>', 

Fig.  174 


cases  the  method  has  the  stamp  of  being  scientific,  but  it 
is  unscientific  and  has  the  stamp  of  ignorance  to  use  the 
method  when  the  tissues  are  excessively  soft  and  stability 


CONSTRUCTING  VACUUM  CHAMBERS 


293 


is  the  result  desired.  The  second  method  consists  of  attach- 
ing soft  vulcanite  disks  to  depressions  in  the  maxillary  or 
mandibular  surface  of  the  denture  (Fig.  175).  The  rationale 
of  this  method  is  that  the  thin  pliable  disk,  by  the  aid  of 
moisture,  easily  conforms  to  a  surface  covered  with  thin  and 
tense  mucous  tissue,  then  as  traction  is  applied  to  the 
denture  it  draws  the  centre  of  the  disk  away  from  the  tissue, 
thus  forming  a  vacuum.  It  is  obvious  that  such  a  denture 
is  pendently  seated,  but  that  it  will  require  much  force  to 
remove  it  from  the  mouth.    The  mouths  where  such  methods 


are  indicated  are  rare,  and  to  insert  such  unsanitary  appliances 
when  other  methods,  properly  used,  would  meet  the  require- 
ments is  reprehensible.  As  velum  rubber  contains  but  two- 
fifths  as  much  sulphur  as  hard  vulcanizable  rubber  it  is 
evident  that  the  soft  vulcanite  is  but  two-fifths  "cured;" 
therefore,  it  is  easily  understood  why  the  material  is  so  much 
less  durable,  swells,  changes  form,  acquires  an  ofl'ensive  odor, 
and  requires  renewal  every  few  months.  "Velum  rubber" 
should  never  be  used  in  the  mouth  except  where  the  con- 
ditions cannot  be  met  by  other  means,  and  then  it  should  be 
renewed  often. 


294 


RETENTION  OF  ARTIFICIAL  DENTURES 


Speyer's  Cohesion-surface  Forms. — Speyer's  "Cohesion- 
surface  forms"  (cohesion  improperly  used)  is  heavy  tinfoil, 
the  surface  of  which  is  covered  with  minute  papilliform 
prominences.  The  claim  of  strong  adhesion  due  to  the  pecu- 
liar conformation  is  hardly  tenable;  however,  they  are  decora- 
tive and  are  satisfying  to  the  mind  of  some  patients;  never- 
theless, the  same  thickness  of  plain  tinfoil  would  produce  the 
same  physical  results.  Fig.  176  shows  the  material  as  it 
is  procurable  at  the  supply  houses.  It  should  be  used  only 
upon  the  surface  requiring  relief.  A  half  sheet  properly 
shaped  is  usually  enough  for  one  denture.     Fig.  177  is  a 


Fig.  176 


Fig.  177 


section  of  the  "cohesion-surface  forms"  enlarged  four  times 
to  better  show  its  construction.  These  "cohesion-surface 
forms"  were  used  in  several  of  the  dentures  illustrated  in 
this  book.  "Contraptions"  for  retaining  artificial  den- 
tures, as  sometimes  seen  in  supply  houses,  are  not  only 
injurious  to  the  mouth,  but  often  a  detriment  to  retention. 
The  denture  is  often  strongly  retained  in  spite  of  the  appli- 
ance. The  student  should  be  able,  with  his  knowledge  of 
anatomy  and  the  laws  of  physics,  to  detect  the  unscientific 
things. 

Vacuum  Chambers  Indicated. — (1)  Vacuum  chambers  are 
indicated  in  partial  upper  dentures  when  other  methods  to 


TENSOFRICTION  295 

be  described  cannot  be  used  to  advantage.  (2)  Full  upper 
cases  where,  owing  to  the  fulness  of  the  anterior  process,  the 
labial  flange  of  the  base-plate  is  not  used.  (3)  In  all  full 
upper  cases  where  the  patient  is  a  novice  in  wearing  artificial 
dentures.  (4)  Very  flat  vaults  with  thin,  tense  tissues.  The 
shallow  chamber  {-j^-^  of  an  inch)  is  indicated  for  these  cases, 
unless  relief  spaces  are  indicated  over  the  raphe,  when  it  will 
answer  the  double  purpose  of  relief  and  chamber.  (5)  Flat 
vaults  with  an  excess  of  soft  tissue,  where  for  any  reason 
peripheral  adaptation  and  compression  has  not  been  obtained. 
These  cases  will  require  a  deep  chamber  of  ^j  to  yV  of  an 
inch  in  thickness. 

TENSOFRICTION 

This  term  is  used  to  cover  all  those  methods  where  reten- 
tion is  obtained  by  contact,  but  the  surface  of  the  contact 
is  too  insignificant  to  constitute  a  factor.  It  includes  all 
forms  of  clasps,  removable  plate-bridge  attachments,  spiral 
springs,  and  spring  plates.  It  implies  that  retention  is 
obtained  by  friction  through  tension.  The  simplest  form 
of  tensofriction  is  the  spring  clasp,  in  which  the  narrow 
strip  of  metal  grips  the  tooth  by  friction  through  the  tension 
in  the  metal. 

It  is  not  relevant  in  this  book  to  discuss  that  class  of 
partial  dentures  known  as  "bridge-work;"  only  to  say  that 
there  is  a  large  class  of  cases  where  the  best  interests  of  the 
patient  will  be  subserved  with  a  plate  denture.  In  all  cases 
the  cosmetic  effects  of  a  plate  is  equal  to  and  in  many  places 
far  superior  to  a  bridge. 

It  is  a  good  rule  to  consider  that  a  natural  tooth  that  is 
or  can  be  made  comfortable  and  useful  to  the  patient  is  far 
more  valuable  than  an  artificial  one.  However,  the  con- 
ditions may  be  such  that  a  remaining  tooth  or  two  in  the 
upper  maxillae  may  be  more  of  a  detriment  to  the  wearer  of 
an  artificial  denture  than  their  loss;  l)ut  it  is  always  a  subject 
for  serifjus  thought. 

In  a  few  cases  the  partial  denture  may  be  retained  by 


296  RETENTION  OF  ARTIFICIAL  DENTURES 

atmospheric  pressure,  adhesion  by  contact,  or  by  the  spring 
plate;  but  usually  the  best  results  are  obtained  by  the  use 
of  clasps. 

CLASPS 

There  is  an  unjust  prejudice  in  the  minds  of  some  den- 
tists against  the  use  of  clasps.  This  is  probably  due  to  an 
improper  knowledge  of  their  advantages  and  disadvantages; 
also  an  insufficient  knowledge  of  the  mechanical  principles 
involved  and  their  practical  application.  The  advantages  of 
the  clasps  may  be  summed  up  in  the  statement  that  there  is 
no  method  by  which  a  partial  plate  denture  may  be  retained 
with  so  much  comfort  and  usefulness  to  the  patient  as  with 
clasps.  This  implies  that  the  conditions  are  favorable  and 
the  method  is  properly  applied.  The  disadvantages  are  that 
in  some  cases  the  method  should  not  be  used  because  the 
remaining  teeth  are  not  healthful  nor  favorably  located  and 
may  be  of  improper  conformation.  The  last  condition  must 
preclude  clasps.  The  principal  argument  used  by  those  who 
object  to  the  use  of  clasps  is  that  they  cause  disintegration, 
of  the  teeth  to  which  they  are  attached.  The  writer  emphat- 
ically states  that  the  cases  in  which  this  is  necessarily  so 
are  very  few  indeed;  but  that  most  of  these  unfortunate 
occurrences  are  due  to  imperfect  knowledge  and  manipu- 
lation of  the  dentist.  It  is  awe-inspiring  to  see  how  some 
of  these  men  who  throw  up  their  hands  in  holy  horror  at  the 
idea  of  clasping  a  tooth  will,  in  a  few  minutes,  ''disinte- 
grate" a  sound  tooth  to  the  extent  of  removing  the  whole 
crown  and  pulp  for  the  purpose  of  attaching  a  bridge. 
Some  argue  that  a  tooth  should  never  be  clasped  until  it  has 
been  crowned.  Why  not  wait  until  the  necessity  arises,  and 
then  fill  or  crown  as  may  be  necessary?  "Consistency  is  a 
jewel."  The  question  should  be:  How  can  a  patient  derive 
the  greatest  amount  of  service  from  a  tooth?  not.  How  can 
the  tooth  be  preserved  the  greatest  length  of  time  ?  A  tooth 
is  of  value  only  as  it  is  of  service. 

Names. — There  are  various  forms  of  clasps.  A  stay  clasp 
is  one  that  rests  upon  one  side  and  perhaps   two  angles 


CLASPS 


297 


of  a  tooth,  and  is  used  as  a  bearing  for  a  spring  plate.  A 
spring  clasp  is  one  that  rests  upon  at  least  two  sides  and  three 
angles  of  a  tooth.  Rigid  clasps  are  clamping  devices  that 
telescope  specially  constructed  artificial  crowns.  A  ferrule 
is  a  continuous  band  about  the  tooth. 

Stay  Clasps. — The  stay  clasp  is  represented  in  vulcanite 
work  by  the  thickened  edge  of  the  spring  plate.  The  name 
is  especially  applied  to  the  short  clasps  used  to  stay  mental 
plates.  This  means  may  be  used  to  support  a  spring  plate 
denture  carrying  any  or  all  of  the  six  anterior  teeth,  provided 

Fig.   178 


the  bicuspids  and  molars  are  of  proper  form  and  alignment. 
The  one  essential  factor  for  retaining  a  denture  by  the 
spring  plate  method  is  that  the  distance  across  the  vault 
from  the  bicuspids  upon  one  side  to  the  bicuspids  upon  the 
other  side  of  the  arch  shall  be  greater  at  the  gum  margin 
than  at  some  other  portion  of  the  crowns  of  the  teeth. 
When  the  remaining  teeth  have  the  conformation  and 
alignment  imi)lied  in  the  preceding  statement,  a  plate  of  a 
"horseshoe"  shape,  having  perfectly  adapted  thickened 
edges  for  vulcanite  (Fig.    178),  or  metal  stay  clasps  (Fig. 


298 


RETENTION  OF  ARTIFICIAL  DENTURES 


179),  may  be  sprung  over  the  bulbous  portion  of  the 
teeth.  It  will  then  rest  in  contact  with  the  teeth,  but  with- 
out lateral  pressure.  It  can  only  be  removed  by  springing 
the  heels  of  the  plate  inward.  Should  one  or  more  of  the 
retaining  teeth  be  tilted  lingually  it  will  interfere  with  this 
method  of  retention.  Perfect  adaptation  to  the  cervical 
third  of  the  lingual  surface  is  essential,  and  cannot  be 
obtained,  or  at  least  retained,  if  there  is  an  excessive  inclining 


Fig.   179 


of  some  of  the  teeth.  There  are  cases  where  adaptation  can 
be  made  to  the  middle  third  without  contact  with  the 
cervical  third.  This  method  is  especially  advisable  where 
the  conditions  are  favorable  and  there  are  no  spaces  for 
spring  clasps,  or  the  spring  clasp  would  be  unsightly. 

Spring  Clasp. — Probably  the  principal  reason  for  the 
condemnation,  by  so  many  dentists,  of  the  spring  clasp  is 
a  lack  of  appreciation  of  the  physical  laws  underlying  their 
use    and    construction,    and    the    manipulative    ability    to 


CLASPS 


299 


properly  adjust  them  even  after  the  principles  involved  are 
comprehended.  Doubtless  there  is  no  place  in  dentistry 
where  there  is  so  varied  an  application  of  the  physical  laws 
of  leverage  as  in  the  retention  of  artificial  dentures;  both 
full  and  partial  cases. 

The  Form  of  Tooth  for  Spring  Clasp. — What  is  commonly 
called  a  bell-shaped  tooth  is  the  ideal  form  (Fig.  180). 
The  greatest  diameter  of  such  teeth  is  from  one-half  to  two- 
thirds  the  distance  from  the  gum  line,  or  gingiva,  where  there 
is  recession  of  gum  tissue,  to  the  occlusal  surface  of  the 


tooth.  This  being  true,  it  follows  that  bicuspids  and  some 
of  the  molars  only  are  suitable  for  clasps;  and  these  must 
be  of  more  or  less  i)ronounced  nervous  temperament  type. 

Choice  of  Teeth  for  Clasps. — Conditions  permitting,  the 
first  choice  for  a  tooth  to  clasp  is  the  second  bicuspid,  the 
second  choice  is  the  first  molar,  and  the  last  choice  is  the 
first  bicuspid.  Any  other  placing  of  clasps  is  not  ideal, 
and  will  be  resorted  to  only  because  of  necessity.  Clasps 
may  be  placed  upon  third  molars  and  cuspids,  or  one  of 
each;  but  they  will  be  so  placed  because  there  is  no  other 
alternative. 


300 


RETENTION  OF  ARTIFICIAL  DENTURES 


The  Portion  of  the  Circumference  of  the  Tooth  Clasped. — 
The  spring  clasp  should  cover  two  sides  and  three  angles  of 
the  tooth  (Fig.  181),  and  be  placed  upon  the  distal  and 
lingual  surfaces  of  the  bicuspids  and  the  mesial  and  lingual 
surfaces  of  the  molars.  By  this  arrangement  the  clasps  are 
placed  at  or  near  the  centre  of  leverage  and  as  inconspicu- 
ously as  possible. 

Fig.   181 


The  Longitudinal  Portion  of  Tooth  Clasped. — The  pressure 
must  be  upon  the  incline  toward  the  cervix  (Fig.  182,  a). 
Should  the  excess  of  pressure  be  upon  the  incline  toward 
the  occlusal  end  of  the  tooth,  the  plate  will  be  displaced 
(Fig.  182,  h) ;  therefore,  the  clasp  is  placed  over  the  middle 
third  of  the  crown  of  the  tooth.  Often  the  tooth  is  not  an 
ideal  one,  and  is  so  formed  that  it  becomes  necessary,  if  a 
clasp  is  to  be  used,  to  carry  it  to,  or  even  below,  the  free 


CLASPS  301 

margin  of  the  gum.  These  are  the  cases  wherein  there  is 
danger  of  disintegration  of  the  clasped  tooth.  Some  teeth 
thus  clasped,  that  are  of  a  very  dense  nature  and  not  prone 
to  decay,  may  become  very  sensitive,  which  can  usually 
be  overcome  by  applying  silver  nitrate,  50  per  cent,  solution. 
Should  the  tooth  belong  to  the  class  commonly  called  soft 
and  chalky,  and  the  secretion  be  in  an  abnormal  condition, 
they  may  disintegrate  very  rapidly;  the  tooth  should  then 
be  filled  or  crowned,  as  may  be  indicated.  It  is  not  often  we 
have  all  these  untoward  conditions;  therefore  the  method 
should  not  be  condemned  because  of  these  exceptional  cases. 
Where  the  teeth  are  of  suitable  length  and  form,  even  though 

Fig.  182 


the  structure  may  be  poor  and  the  secretion  vitiated,  if 
the  clasps  are  properly  made,  placed,  and  cleansed,  there 
will  be  very  little  danger  of  decay.  In  all  cases  it  is  best 
to  keep  the  clasps  as  far  from  the  gum  as  the  conditions  will 
permit. 

Forms  and  Material  for  Clasps.— Clasps  are  made  of  either 
round,  fiat,  or  half-round  clasp  gold.  A  good  formula  for 
clasp  gold  is:  Pure  gold,  twenty  parts;  pure  copper,  two 
parts;  pure  silver  and  platinum,  of  each,  one  part. 

Rointd  aiafips.— The  round  clasp  should  be  made  of  IS- 
or  possibly  20-gauge  clasy)  gold  wire,  and  may  be  used 
either  as  a'single  or  double  strand  (Fig.  1S3).  The  advantage 
claimed  for  the  wire  clasp  is  the  slight  contact  with  the 
tooth.  The  disadvantages  are:  The  thickness  of  the  wire 
will  often  prevent  it  being  placed  between  the  natural  teeth ; 


302 


RETENTION  OF  ARTIFICIAL  DENTURES 


it  has  not  the  retention  power  of  the  flat  clasp  unless  it  is 
placed  very  near  the  centre  of  leverage  (this,  however,  does 
not  apply  to  the  double  strand  wire  clasp);  and  it  is  often 
more  unsightly  than  the  flat  clasp. 

Flat  Clasp. — The  flat  clasp  is  made  of  26-gauge  clasp 
gold,  and  from  -^^  to  |  inch  in  width,  usually  about  i  to  ^ 
inch  (Fig.  184).  The  advantages  of  the  flat  clasp  are:  (1) 
Its  thinness — when  necessary  to  pass  between  the  natural 
teeth,  the  necessarj^  space  can  be  secured  by  slight  wedging; 

(2)  there  is  no  form  of  clasp  that  is  so  universally  applicable; 

(3)  it  gives  great  stability  to  the  denture;  and  (4)  it  is  not 
liable  to  be  broken.     The  disadvantage  is  that  the  broad 


Fig.  183 


Fig.   184 


surface  of  tooth  substance  covered  is  favorable  for  decay, 
and  necessitates  the  best  judgment  upon  the  part  of  the 
operator  in  placing  the  clasp,  also  care  upon  the  part  of 
the  patient  to  keep  it  clean. 

Half-round  Clasps. — ^The  half-round  clasp  is  made  of 
half-round  clasp  gold  wire  and  has  the  disadvantages  of 
both  the  round  and  flat  clasps  without  their  advantages. 

Rigid  Clasps. — These  clasps  may  be  made  of  flat  clasp  metal 
or  18-carat  gold  plate;  they  are  usually  as  broad  as  the 
length  of  the  crown  of  the  tooth  will  permit;  they  are  of 
sufficient  length  to  cover  at  least  one  side  and  two  angles 
of  the  tooth,  and  the  ends  are  either  bent  L-shape  to  slide 
over  parallel  longitudinal  ridges  or  cleats  upon  gold  crowns 


CLASPS 


303 


(Fig.  185)  (Bryant  method),  or  they  are  provided  with  a 
thick  end  adapted  to  parallel  longitudinal  grooves  in  pref- 
erably porcelain  crowns  (Fig.  1S6)  (Swartz  method). 


Fig.  185 


Fig.  186 


Ferrules. — Ferrules  are  especially  indicated  where  the 
natural  teeth  are  remaining  upon  one  side  of  the  maxillae  or 
mandible  and  absent  on  the  other.  The  ferrule  is  superior 
to  the  spring  clasp  for  this  class  of  cases  because  of  its 
unyielding  form  (Fig.  187).  Where  conditions  are  favorable, 
two  or  possibly  three  may  be  used  to  advantage.     Sometimes 

Fig.   187 


extensions  may  be  attached  to  the  buccal  surface  of  the 
ferrule  to  act  as  clasps  upon  the  proximating  teeth.  Should 
there  not  be  sufficient  space  between  the  tooth  to  be  ferruled 
and  the  proximating  teeth  to  pass  a  2()-gauge  plate,  it  will 
be  necessary  to  gain  such  space  by  wedging  with  tape  until 
such  space  is  obtained,  when  it  will  be  maintained  by  the 
ferrule. 


304 


RETENTION  OF  ARTIFICIAL  DENTURES 


PRINCIPLES  INVOLVED  IN  RETENTION 

There  are  two  propositions  to  be  considered,  first,  balancing 
the  plate,  and  second,  gripping  the  tooth  or  teeth. 

Balancing  the  Plate. — We  may  consider  each  side  of  a 
partial  plate  as  a  lever,  the  tooth  clasped  as  the  fulcrum, 
and  the  plate  extending  either  way  from  the  clasp  as  the 
arms  of  the  lever.  Fig.  188  represents  a  partial  upper  of  a 
horseshoe-shape  carrying  the  six  anterior  teeth  and  the 
wings  extending  backward  to  the  third  molars.    It  is  easily 

Fig.  188 


imagined  what  the  result  would  be  should  an  attempt  be 
made  to  retain  this  denture  by  a  single  strand  wire  clasp 
placed  upon  the  third  molars;  also,  should  the  wire  clasps  be 
replaced  with  broad  flat  clasps  accurately  fitted  to  the 
surface  of  the  teeth.  With  the  broad  clasps,  the  anterior 
portion  of  the  plate  would  be  held  in  place  for  a  time  at 
least,  but  the  long  leverage  and  the  weight  of  the  porcelain 
teeth  would  place  such  a  strain  upon  the  third  molars  that 
they  would  become  very  sore  and  loosened  in  their  sockets. 
If  these  clasps  are  replaced  with  single  strand  wire  clasps 
upon  the  second  bicuspids,  the  plate  will  be  securely  held  in 
place  and  with  the  minimum  strain  upon  the  clasped  teeth, 
because  the  clasps  are  at  the  centre  of  leverage.    This  demon- 


PRINCIPLES  INVOLVED  IN  RETENTION         305 

strates  why  it  is  necessary  to  extend  the  base-plate  some 
distance  back  of  the  clasped  teeth.  This  centre  also  explains 
why,  if  a  clasp  is  placed  upon  a  third  molar  upon  one  side, 
a  clasp  should  be  placed  upon  the  first  bicuspid,  or  even  the 
cuspid,  upon  the  other  side  of  the  arch.  It  is  obvious  that 
the  best  results  are  obtained  when  there  is  a  tooth  for  clasp- 
ing upon  each  side  of  the  mouth.  While  two  teeth  for 
clasping  are  most  desirable,  if  the  conditions  for  retaining 
a  denture  by  adhesion  by  contact  are  very  unfavorable,  a 
single  bicuspid  or  molar  may  be  of  much  assistance  (Fig.  1S9) ; 
and  on  the  mandible  even  a  single  cuspid  should  be  utilized. 

Fig.    189 


Gripping  the  Tooth. — There  are  many  cases  of  failure  in 
clasp  dentures  due  to  carelessness  or  slight  accidents  in 
adjusting  the  clasps  to  the  teeth.  The  clasps  should  be  so 
adjusted  to  the  teeth  that  there  will  be  no  lateral  strain. 
Theoretically,  when  the  mouth  is  at  rest  there  should  be  no 
strain  upon  the  clasped  teeth,  because  the  upper  plate 
(even  though  a  narrow  rim)  should  have  sufficient  adhesion 
by  contact  to  sustain  its  weight,  and  the  lower  plate  is  held 
in  place  by  gravitation;  hence  the  clasps  are  a  reserve  force 
for  wrirk.  Fig.  190,  r/,  represents  a  broad  flat  spring  clasp 
improperly  adjusted.  The  linguocervical  edge  of  the  clasp 
20 


306 


RETENTION  OF  ARTIFICIAL  DENTURES 


rests  upon  the  tooth,  while  the  Hnguo-occlusal  edge  is  some- 
what distant  from  the  tooth.  When  the  arms  of  the  clasp 
are  bent  inward  so  as  to  cause  the  clasp  to  grip  the  tooth, 
the  linguo-occlusal  edge  will  approach  the  tooth,  and  the 
base-plate,  which  represents  the  long  arm  of  a  lever,  will  be 
tilted  away  from  the  vault  of  the  mouth,  as  shown  by  the 
dotted  line.  If  the  reverse  of  these  conditions  exists  (Fig. 
190,  b),  that  is,  the  linguo-occlusal  edge  rests  upon  the  tooth 
and  the  linguocervical  edge  stands  away  from  the  tooth, 
then  when  the  spring  of  the  arms  draws  the  clasp  firmly  to 
the  tooth,  the  plate  will  be  held  securely  against  the  vault 
of  the  mouth;  there  will  be,  however,  a  lateral  strain  upon 
the  tooth,  tending  to  move  the  apex  of  the  root  of  the  tooth 


F 

iG.  190 

L  )/- 

C~~~^' 

f  ■ 

'  Czr 

7 

V^-^'v- 

1 

toward  the  vault.  If  either  of  these  imperfect  conditions 
is  to  exist,  it  had  better  be  the  latter,  because  the  denture 
will  be  held  firmly  in  place,  and  in  time  the  tooth  will  be 
adjusted  to  the  existing  conditions;  although  sore  during  the 
orthodontic  process. 

Adaptation  of  the  Clasps  to  the  Tooth. — There  are  two 
methods  of  adapting  clasps:  (1)  The  clasp  is  formed  by 
pliers  to  approximately  a  close  adaptation,  so  that  it  will  be 
uniformly  supported  yet  not  so  close  but  that  the  fluids  of 
the  mouth  can  pass  freely  between  the  metal  and  tooth. 
(2)  A  piece  of  thin  pure  gold  or  platinum  (36  gauge)  is 
accurately  fitted  to  the  tooth;  a  strip  of  clasp  metal  is  then 
adjusted  as  closely  as  possible  with  pliers  to  the  burnished 


PLIERS 


307 


metal  and  the  two  united  with  wax;  they  are  then  sprung:; 
away  from  the  tooth,  invested,  and  thoroughly  soldered 
together.  It  is  possible,  with  this  perfect  adaptation  of  the 
clasps  to  the  tooth,  the  secretions  being  retained  by  capillary 
attraction  and  not  changed  by  the  fluids  circulating  in  the 
mouth,  that  disintegration  may  be  invited;  but  with  proper 
cleansing  and  removing  the  denture  at  night  almost  no  ill 
effects  will  present. 

Forming  the  Clasps  with  Pliers. — Clasp  gohl  is  very  crys- 
talline, and  when  it  is  rolled  from  the  ingot  into  plate  the 
crystals  are  elongated  into  fibers.  The  metal  is  easily  split 
between  the  fibers;  across  the  fibers  there  is  strength  and 
flexibility,  so  for  this  reason  the  fibers  should  run  lengthwise 
of  the  clasp,  that  is,  around  the  tooth.  Before  forming  the 
clasp  the  metal  should  be  annealed  b\'  heating  to  a  cherry-red 
heat  and  permitting  to  cool  slowly. 


PLIERS 

Two  pairs  of  pliers  are  required.     One  (we  will  call  No.  1) 
with  hawk-bill-shaped   beaks,  the  under  smaller  than  the 

Fig.   I'Jl 


over  beak  and  oval  or  round  in  its  cross-section,  while  the 
over  beak  is  flat  on  the  under  surface  of  its  cross-section 
(Fig.  191).    The  other  pair  of  plyers  (No   2)  is  the  ordinary 


308 


RETENTION  OF  ARTIFICIAL  DENTURES 


clasp-forming  variety,  having  a  round  and  a  concave  blade 
(Fig.  192),  No.  1  pliers  is  for  general  utility,  and  with  it 
most  of  the  shaping  of  the  clasps  is  done.  It  gives  the 
concavoconvex  form  to  the  cross-section  of  the  clasp,  and  in 


connection  with  the  fingers  give  the  general  outline  of  the 
tooth.  The  No.  2  plyers  is  better  adapted  to  bending  the 
clasp  to  sharp  angles,  depressing  a  bulging  portion  or  denting 
the  edge  of  a  clasp. 


Fig.   193 


Fig.  194 


Attaching  the  Clasp  to  the  Plate. — In  gold  work  the  clasp 
is  either  soldered  to  the  plate  (Fig.  194,  a),  or  connected 
to  the  plate  by  means  of  one  or  two  standards  (Fig.  193,  a 
and  b).  For  vulcanite  work  a  tang  is  soldered  to  the  clasp 
(Figs.  183  and  184),  after  which  the  base-plate  may  be 
extended  any  distance  to  grip  the  tang.  Fig.  184  b,  shows 
union  of  clasp  and  tang. 


CEMENTATION  309 


LOCATION  OF  ATTACHMENT  UPON  CLASP 

The  attachment  to  the  clasp  should  be  one-eighth  to  three- 
sixteenths  of  an  inch  wide,  and  should  be  placed  as  near  the 
middle  of  the  long  way  of  the  clasp  as  the  setting  of  the  teeth 
will  permit.  By  this  arrangement  a  spring  clasp  will  not  be 
converted  into  an  unwieldy  stay  clasp.  Fig.  194,  a,  shows 
the  right  way  to  form  the  attachments  while  Fig.  194,  h, 
illustrates  a  wrong  way. 

Conclusion. — Clasps  properly  conceived  and  formed  are  a 
blessing  to  both  patient  and  prosthetist,  but  improperly 
used  are  vexatious  to  the  dentist  and  a  detriment  to  the 
victim.  The  retention  of  artificial  dentures  either  partial  or 
full  is  a  profound  subject  for  thought,  and  worthy  the  best 
eflForts  of  the  prosthetist. 


CEMENTATION 

This  term  is  used  to  denote  that  an  adhesive  substance, 
as  cement,  is  used  as  the  means  of  retention  for  crowns, 
bridges,  and  the  so-called  "alveolar  dentures."  Crowns  and 
spanning  bridges  are  clearly  out  of  the  scope  of  this  book, 
while  removable  bridge-work  is  on  the  border  line  between 
bridge-work  and  plate-work.  A  spanning  bridge  with  one 
or  more  saddle  abutments  is  clearly  a  bridge.  A  saddle 
extending  under  the  entire  denture  is  but  an  extension  of  the 
saddle  abutment,  therefore  there  is  no  clear  line  of  demar- 
cation between  bridge-work  and  plate-work.  However,  a 
base-plate,  of  whatever  material,  depending  upon  telescoping 
crowns,  bar  and  slot,  tube  and  split  pin,  or  a  pin  or  l)all 
with  slit  tube  attachments,  are  so  intimately  associated  with 
crown  work  that  they  will  not  be  further  considered  in  this 
book. 

Except  to  condemn,  the  atrocities  perpetrated  under  the 
alluring  name  "alveolar  dentistry"  arc  unworthy  of  con- 
sideration in  any  book. 


CHAPTER    VIII 

PORCELAIN  TEETH 

History. — The  late  Professor  Essig  states  in  the  chapter  on 
Porcelain  in  the  American  Text-book  of  Prosthetic  Dentistry 
that  the  history  of  the  first  use  of  mineral  in  place  of  animal 
substances  for  artificial  teeth  is  wrapped  in  obscurity.  One 
of  the  early  recorded  suggestions  along  this  line  is  that  of 
Guillemeau,  in  1710,  who  proposed  a  paste  compound  of 
white  wax,  gum  elemi,  white  mastic,  coral,  and  pearl.  Pierre 
Fauchard,  in  Le  Chirurgien  Dentiste,  1728,  suggests  the  use 
of  artificial'  enamel  for  this  purpose. 

The  idea  of  "hard  mineral  teeth"  is  to  be  attributed  to 
M.  Duchateau,  an  apothecary  of  St.  Germain-en-Laye, 
near  Paris.  He  conceived  the  idea,  in  1774,  of  constructing  a 
plate  in  porcelain,  molding  it  after  the  form  of  his  ivory  one. 
M.  Duchateau  took  as  an  associate  a  dentist  of  Paris  by  the 
name  of  M.  Dubois  de  Chemant.  M.  de  Chemant  improved 
the  porcelain,  and  in  1790  obtained  a  patent  from  Louis 
XVI  for  his  process.  Dubois  Foucou,  dentist  to  the  king, 
became  interested  in  de  Chamant's  work,  made  improvements 
in  the  material,  and  made  public  the  first  description  of  the 
method  for  making  mineral  teeth.  In  1808,  Fonzi,  another 
dentist  of  Paris,  first  made  separate  individual  teeth,  and 
also  baked  small  pieces  of  platinum  in  them  to  serve  as  a 
means  of  attachment  to  the  plate. 

De  Chemant  moved  to  London  in  1791  and  became  asso- 
ciated with  Claudius  Ash,  and  for  many  years  experimented 
in  and  manufactured  porcelain  teeth. 

Porcelain  teeth  were  not  introduced  into  America  until 
about  1817.  The  first  use  of  them  of  which  we  have  knowl- 
edge was  by  A.  A.  Plantou,  a  Frenchman,  who  began  the 


COMPOSITION  OF  PORCELAIN  311 

practice  of  dentistry  in  Philadelphia  about  that  time.     He 
commenced  the  manufacture  of  mineral  teeth  about  1820. 

Charles  W.  Peale,  in  1822,  and  Samuel  W.  Stockton,  in 
1825,  were  the  next  after  Plantou  to  manufacture  porcelain 
teeth,  and  they  were  soon  followed  by  many  others.  By  the 
year  1838  mineral  teeth  were  in  general  use.  About  this 
year  Dr.  Elias  \Yildman,  of  Philadelphia,  succeeded  in 
improving  the  material,  so  that  it  would  stand  the  high  heat 
of  soldering,  and  the  texture  and  life-like  appearance  to  such 
an  extent  that  it  has  been  said  that  it  remains  unexcelled 
to  the  present  day.  To  him  has  been  accredited  the  honor  of 
placing  the  manufacture  of  porcelain  teeth  on  a  scientific 
basis. 

COMPOSITION  OF  PORCELAIN 

Definition. — Porcelain  is  divided  into  three  classes,  as 
hard,  natural  soft,  and  artificial  soft.  Dental  porcelain 
belongs  to  the  subdivision  hard  porcelain,  and  may  be  defined 
as:  A  solidified  suspension  of  one  or  more  unfused  silicious 
substances  in  a  fused  silicate.  Porcelain  is  high  or  low  fusing, 
dependent  upon  the  quality  and  quantit}'  of  the  basic  ingre- 
dient. The  material  commonly  called  glass  is  fused  silicious 
salts;  therefore,  all  porcelains  may  be  converted  into  glass 
by  sufficient  fusing. 

Materials. — The  materials  entering  into  dental  porcelain 
are  feldspar,  silica,  kaolin  or  clay,  alkalies,  and  pigments. 
The  pigments  used  are  made  of  titanium,  cobalt,  iron,  tin, 
gold,  and  platiiuim. 

Feldspar. — This  is  generally  spoken  of  as  a  double  silicate 
of  aluminum  and  potassium,  and  is  represented  by  the 
formula  AL^O,  K,-0,  OSiO..  The  best  feldspar  is  found  in 
the  neighborhood  of  Wilmington,  Del.  It  presents  a  distinct 
cleavage,  and  when  broken  splits  into  plates  of  more^or  less 
magnitude.  It  is  of  an  indefinite  color,  l)etwecii  yellow  and 
pink,  but  when  fused  in  the  furnace  it  becomes  transparent 
and  colorless,  and  if  not  exposed  to  a  too  prolonged  or  an 
excessively   high   temperature  it  retains  its  original   form 


312  PORCELAIN  TEETH 

without  rounding  at  the  corners;  this  is  one  of  the  tests  of 
good  feldspar.  There  are  several  deposits  of  this  mineral 
in  eastern  Pennsylvania,  which,  though  beautiful  and  trans- 
parent in  appearance,  have  been  found  to  be  entirely  unfit 
for  dental  porcelain  because  of  their  opaque-white  color 
when  fused  in  the  furnace.  The  preparation  of  the  spar 
consists  of  selecting  suitable  rock  (some  of  the  spar  from  a 
good  quarry  will  not  answer  for  dental  porcelain),  breaking 
it  into  fragments  with  a  steel  and  hammer,  and  grinding  it 
into  powder  in  a  Wedgwood  mortar.  The  material  is  sifted 
at  intervals  through  a  No.  10  bolting-cloth  sieve.  The  grind- 
ing should  not  be  carried  too  far,  or  its  translucency  may  be 
greatly  lessened. 

Silica  (Si02). — This  material,  sometimes  called  quartz, 
occurs  in  crystalline  and  amorphous  forms;  it  is  colorless, 
infusible  at  ordinary  temperature,  insoluble  in  water  and 
all  acids  except  hydrofluoric.  The  amorphous  and  gelatin- 
ous varieties  are  partially  soluble  in  alkaline  carbonates, 
but  quite  soluble  in  caustic  alkalies.  Silica  combines  with 
the  bases  to  form  silicates. 

The  purest  natural  form  of  silica  is  the  transparent  and 
colorless  variety  of  quartz  known  as  rock-crystal.  Without 
transparency  and  crystalline  structure,  silica  is  met  with  in 
the  form  of  chalcedony  and  carnelian,  agate,  cat's  eye,  onyx, 
opal,  and  other  precious  stones.  Sand,  of  which  the  white 
varieties  are  pure  silica,  appear  to  have  been  formed  by  the 
disintegration  of  silicious  rock.  The  yellow  and  brown  dis- 
coloration is  due  to  the  pressure  of  oxide  of  iron. 

Silica  is  used  for  the  purpose  of  giving  stability  and  firm- 
ness to  porcelain,  and  its  infusibility  stiffens  and  keeps  the 
other  materials  in  shape  so  that  an  object  made  of  porcelain 
may  preserve  its  molded  form  while  exposed  to  the  high  tem- 
perature during  the  process  of  firing.  For  these  reasons  it  is 
incorporated  with  feldspar  and  clay,  and  is  looked  upon  as 
the  "main  prop  in  tooth  body." 

The  quartz  is  crushed  and  ground  in  a  Wedgwood  mortar 
until  it  will  pass  through  a  No.  10  bolting-cloth  sieve,  when 
it  is  reduced,  under  water,  to  an  impalpable  powder. 


COMPOSITION  OF  PORCELAIN  313 

Kaolin. — Kaolin  is  the  purest  quality  of  clay  freed  from 
such  impurities  as  sand  and  mica  by  careful  washing.  It 
is  a  hydrated  silicate  of  alumina,  and  may  be  represented 
by  the  formula  (2A1,03,  SSiO.)  +  H2O.  It' is  formed  by  the 
long  continued  action  of  air  and  water  upon  granite  and 
feldspar  rock.  The  disintegration  is  probably  due  to  both 
mechanical  and  chemical  causes. 

Clay  is  infusible  in  an  ordinary  furnace  when  heated  alone, 
but  readily  unites  with  feldspar  at  a  high  temperature.  It 
is  an  element  of  strength  in  porcelain. 

German  clay  is  imported  from  Europe  and  is  probably  the 
most  infusible  of  the  clays. 

Alkalies. — Both  of  the  alkali  metals  potassium  and  sodium 
are  used  as  fluxing  material.  Potassium  is  an  essenti;  ' 
element  of  porcelain.  Sodium  could  not  be  substituted  for 
potassium  because  of  the  green  tint  it  imparts  to  the  product ; 
but  in  conjunction  with  potassium  it  is  a  valuable  addition, 
because  it  increases  the  fusibility  without  increasing  the 
amount  of  alkali.  The  potassium  and  sodium  salts  are  all 
soluble  in  water.  It  is  evident  that  this  property  in  artificial 
teeth  is  undesirable,  but  concomitant  with  the  lowering 
of  the  fusing  point  of  the  porcelain.  Therefore,  it  is  logical 
to  conclude  that  the  higher  the  fusion  of  the  porcelain  the 
less  soluble,  and  the  lower  the  fusion  the  more  soluble.  In 
other  words,  the  high  fusing  porcelains  are  practically 
insoluble,  whereas  the  low  fusing  are  liable  to  etch  and  dis- 
integrate in  the  fluids  of  the  mouth.  Undoubtedly  the 
modern  makes  of  artificial  teeth  are  sufficiently  high  fusing 
to  be  insoluble  in  the  mouth;  but  the  porcelains  placed 
upon  the  market  for  the  dentist's  use  in  constructing  bridges, 
crowns,  and  inlays,  excepting  the  highest  fusing  ones,  are 
dangerously  near  the  etching  point.  Material  has  been 
placed  upon  the  market  so  loaded  with  flux  (alkali)  that 
they  soon  prove  to  be  unstable.  In  using  low  fusing  porce- 
lain, to  be  placed  in  the  mouth,  this  j)r()perty  of  solubility 
(etcliingj  must  be  taken  into  account;  as  low  fusion  can  only 
be  produced  by  adding  flux  (however,  excessive  pulverizing 
lowers  the  fusing  point,  also  injures  the  texture),  and  the 
more  flux  the  more  soluble. 


314  PORCELAIN  TEETH 

It  is  interesting  to  study  the  four  essential  elements 
entering  into  porcelain — oxygen,  silicon,  potassium,  and 
aluminum;  one  gas  and  three  solids;  two  non-metals  and 
two  metals.  Of  the  three  solids,  silicon  melts  at  1500°  F., 
potassium  at  144.5°  F.,  and  aluminum  at  1200°  F.  Oxygen  is 
the  most  abundant  and  silicon  second  most  abundant  ele- 
ment, while  aluminum  is  the  most  abundant  metal.  Silicon 
combined  with  oxygen  (silica)  is  almost  infusible  and 
insoluble,  and  there  is  almost  no  expansion  or  contraction 
by  heat.  Aluminum  combined  with  oxygen  (alumina)  is 
highly  refractory  and  non-changeable.  Potassium  combined 
with  oxygen  forms  potassa;  it  fuses  at  a  low  temperature, 
and  is  very  soluble  in  water.  Silica  combined  with  alumina 
forms  kaolin  (clay),  is  refractory,  easily  hydrated,  and 
contracts  in  heating.  Silica  and  alumina  combined  with 
potassa  forms  feldspar,  which  material  forms  the  largest 
portion  of  artificial  teeth. 

Pigment. — The  pigmentary  substances,  titanium,  cobalt, 
iron,  and  tin,  are  used  in  the  form  of  oxide ;  gold  is  used  both 
as  an  oxide  and  in  the  metallic  state;  and  platinum  as  a  fine 
precipitate-platinum  sponge. 

Titanium  oxide  is  the  only  pigment  used  in  the  "body 
porcelain."  It  gives  the  creamy  yellow  color  of  the  dentine. 
It  is  also  used  for  the  yellow  color  of  enamel. 

Cobalt  oxide  produces  the  blue  tints  of  enamel. 

Iron  oxide  is  used  for  certain  gray  tints. 

Tin  oxide  is  used  only  in  combination  with  gold  oxide  as 
purple  of  Cassius  to  produce  the  pink  gum  color. 

Gold  is  used  in  the  metallic  state  for  reddish-brown  tints 
in  enamels. 

Platinum  sponge  produces  gray  tints. 

THE  PROCESS  OF  MANUFACTURE 

The  process  of  manufacturing  artificial  teeth  consists  of 
(1)  preparing  the  stock  material,  (2)  molding,  and  (3)  firing. 

Stock  Material. — The  stock  material  is  first  worked  up 
into  three  forms,  as  body,  frit,  and  enamel. 


THE  PROCESS  OF  MANUFACTURE  315 

Body. — The  body  represents  the  dentine  of  the  natural 
teeth.  It  is  the  highest  fusing  portion  of  the  porcelain.  It 
is  composed  of  feldspar,  silica,  kaolin,  and  titanium  oxide, 
with  a  small  amount  of  starch  to  make  the  material  plastic 
for  molding. 

Each  manufacturer  has  his  secret  formulae,  but  the  fol- 
lowing formula  gives  an  idea  of  the  proportions  of  the 
ingredients:  Kaolin,  1  ounce;  sihca,  3  ounces;  feldspar,  18 
ounces;  titanium  oxide,  65  grains;  starch,  10  grains  to  each 
ounce. 

Frits. — The  frits  are  the  colors  prepared  for  the  enamels. 
They  consist  of  the  pigment  substance  mixed  with  feldspar 
and  flux  ground  exceedingly  fine,  fused  into  a  glass  and 
reground  for  use.  A  topical  formula  would  be:  Platinum 
sponge,  1  pennyweight;  feldspar,  1  ounce;  flux,  20  grains. 

Enamels. — Enamels  are  composed  of  feldspar  to  which 
has  been  added  a  sufficient  quantity  of  frit  and  flux.  A 
typical  formula  for  enamel  is:  Feldspar,  1  ounce;  gold  frit, 
G  grains;  platinum  frit,  4  grains;  flux,  20  grains. 

Flux. — Used  to  lower  the  fusing  point  of  enamels  and 
porcelains.  A  good  formula  is:  Silica,  12  ounces;  glass  of 
borax  (sodium  borate),  3  ounces;  potassium  carbonate, 
3  ounces. 

Molding,— Artificial  teeth  are  made  in  brass  molds.  As 
porcelain  shrinks  in  firing,  the  desired  tooth  is  first  carved 
in  plaster  in  enlarged  form.  From  these  enlarged  forms  brass 
molds  are  produced.  Figs.  195,  196,  197,  and  198  illustrate 
the  molds  used  for  two  sets  of  fourteen  upper  teeth.  The 
molds  are  made  double  for  convenience  in  keying  the  parts 
together. 

The  brass  molds  are  oiled  and  the  platinum  pins  placed 
in  the  little  holes  on  the  pin  side  of  the  molds.  The  point 
enamel  is  then  put  in  the  face  side  of  the  mold  and  arranged 
with  a  small  spatula  to  the  full  thickness  at  the  point  and 
tapered  down  sparingly  toward  the  neck.  A  thin  coat  of 
point  enamel  is  placed  on  the  lingual  side  of  the  front  teeth 
and  on  the  masticating  surfaces  of  the  bicuspids  and  molars. 
Some  makers  of  teeth  use  but  one  enamel;  instead  of  apply- 


316 


PORCELAIN  TEETH 


ing  a  yellow-neck  enamel,  they  allow  the  body  to  show  at 
the  neck  of  the  tooth;  this  is  probably  done  to  save  time  and 
labor,  but  it  does  not  afford  the  best  results  as  to  translucency 
and  natural  appearance. 


Fig.  195 


Fig.  196 


The  body  is  applied  in  small  pieces  slightly  in  excess  of 
the  quantity  needed  for  each  tooth.  These  are  picked  up 
with  a  small  spatula,  formed  into  balls,  and  laid  on  the  pins 
in  the  pin  side  of  the  mold.  The  two  sides  of  the  mold  are 
then  placed  together  and  heavily  pressed.  The  mold  is  then 
removed  from  the  press,  put  in  an  iron  clamp,  and  secured 
firmly  together;  it  is  then  heated  on  a  stove  until  the  mold 


THE  PROCESS  OF  MANUFACTURE 


317 


becomes  hissing  hot,  after  which  it  is  removed  and  allowed 
to  cool  sufficiently  to  handle.  The  mold  is  then  opened  and 
the  teeth  dislodged  and  removed  by  striking  the  mold  with 


Fig.   197 


Fig.  198 


318  PORCELAIN  TEETH 

a  wooden  mallet.  If  the  heating  has  been  carried  to  the 
proper  point,  the  teeth  will  be  hard  enough,  through  the 
agency  of  the  starch  in  the  formula,  to  admit  of  trimming. 
This  is  done  with  fine  files. 

Burning. — In  manufacturing  on  a  large  scale  the  blocks 
are  arranged  in  complete  sets  on  a  fire-clay  slide  covered 
with  coarse  quartz.  These  slides  are  6|  inches  in  width  by 
9|  inches  long;  they  have  raised  edges  to  retain  the  quartz, 
which  serves  as  a  bed  for  the  teeth. 

The  furnaces  used  by  the  large  manufacturers  have  a 
capacity  of  three  or  four  hundred  sets  per  day  for  each  fur- 
nace. The  furnace  has  a  heating  oven  over  the  muffle. 
The  muffle  is  constructed  of  the  best  fire-clay,  27  inches 
long,  8  inches  wide,  5f  inches  high,  and  1\  inches  thick. 
The  muffle  must  be  thoroughly  swabbed  with  clay,  mixed 
thin  with  water,  to  fill  up  all  cracks  or  defects  through  which 
the  gases  from  the  fuel  might  enter  the  muffle.  Such  acci- 
dents are  of  frequent  occurrence  in  burning,  and  are  always 
ruinous  to  the  teeth,  the  gas  generally  imparting  to  them  a 
ghastly  blue  appearance.  The  furnace  has  a  flue  at  the  top 
connected  with  a  smoke  stack,  and  is  heated  with  oil. 

The  slide  containing  the  teeth  is  placed  in  the  heating 
oven  at  the  top  of  the  furnace  before  burning;  this  pre- 
liminary heating  prepares  them  for  the  higher  temperature 
of  the  muffle.  The  length  of  time  required  for  burning  the 
teeth  varies  with  the  heat  of  the  muffle.  About  fifteen 
minutes  is  usually  required.  A  too  rapid  heat  tends  to 
burn  out  or  vaporize  the  color  of  the  enamels.  The  proper 
glazing  of  the  teeth  is  ascertained  by  placing  under  a  gas 
jet.  When  the  burning  is  satisfactorily  accomplished  they 
are  put  in  the  cooling  mufile,  protected  from  air  drafts,  and 
left  undisturbed  until  quite  cold. 

CLASSIFICATION  OF  PORCELAIN  TEETH 

Porcelain  teeth  may  be  divided  into  two  general  classes, 
namely,  plain  and  gum  teeth.  In  the  former  the  crown  of 
the  tooth,  and  sometimes  a  portion  of  the  root,  is  represented, 


CLASSIFICATION  OF  PORCELAIN  TEETH 


319 


whereas,  in  the  latter  class  the  labial  and  buccal  gum  is 
added  to  the  crown.  The  base  upon  which  they  are  to  be 
mounted  and  the  means  of  attachment  to  the  base  further 
divides  them  into  classes  as  follows: 


Plain  Teeth 


Vulcanite  teeth  (Fig.  199). 
Countersunk  pin  teeth  (Fig.  200). 
Pinless  or  diatoric  teeth  (Fig.  201). 
Plate  teeth  (metal  work)  (Figs.  202, 203, 204). 
Continuous  gum  teeth  (Fig.  205). 


Gum  section  teeth  (for  vulcanite)  (Figs.  210 

Gum  Teeth  ■{    ,.      to  215). 

I  bmgle  gum  teeth  (tor  metal  work)  (Figs.  216 
L         and  217). 

Attaching  Teeth  to  Base. — The  means  by  which  the  por- 
celain teeth  are  attached  to  the  base-plate  upon  which 
they  are  mounted  is  usually  two  platinum  pins,  the  headed 
ends  of  which  are  embedded  in  the  substance  of  the  teeth 
and  firmly  fixed  in  it  when  the  porcelain  is  baked.  Platinum 
and  porcelain  have  ver\'  nearly  the  same  coefficient  of  expan- 


FiG.  199 


sion,  so  that  in  a  similar  range  of  temperature  they  approxi- 
mately expand  and  contract  alike,  and  there  is  small  danger 
of  a  cracking  of  the  tooth  or  a  loosening  of  the  pin.  It  must 
be  remembered,  however,  that  the  capacity  for  absorbing 
heat  differs  greatly  with  the  two  substances,  platinum  having 
a  much  higher  specific  heat,  which  fact,  coupled  with  its 


320 


PORCELAIN  TEETH 


greater  conductivity,  makes  it  necessary  that  a  greater 
amount  of  heat  should  be  appHed  to  the  porcelain  when 
teeth  are  subjected  to  high  heat.  The  platinum  does  not 
fuse  at  the  high  temperature  necessary  to  the  baking  of  the 
body  of  the  tooth,  and  its  non-oxidizable  surface  makes  it 
possible  for  the  porcelain  to  adhere  to  it  with  considerable 
tenacity.  One  manufacturer  alloys  iridium  in  small  amount 
with  the  platinum  to  give  the  pins  greater  rigidity  and 
tensile  strength. 

Fig.  200 


The  great  cost  of  platinum  has  been  responsible  for  many 
attempts  either  to  substitute  other  and  less  expensive  metals 
for  it,  or  to  reduce  the  amount  of  metal  used  for  the  attach- 
ment in  the  tooth,  or  to  dispense  with  the  pins  altogether. 
The  less  expensive  metal  usually  employed  is  nickel  or  some 
of  its  alloys,  but  as  these  readily  oxidize  during  the  baking, 
the  intimacy  of  the  union  between  pin  and  tooth  cannot  be 
so  close  as  where  platinum  is  used.  The  discoloration  of 
the  tooth  from  the  dissolved  oxides  of  the  pins  is  frequently 
sufficient  in  amount  to  be  objectionable,  and  the  low  fusing 


CLASSIFICATION  OF  PORCELAIN  TEETH 


321 


body  which  is  necessary  with  teeth  of  this  sort  is  not  so  strong 
as  that  which  may  be  baked  on  platinum  pins.  The  attach- 
ment of  pins  of  base  metal  to  platinum  anchorage  baked  in 
the  tooth  by  soldering  the  pin  to  the  anchorage  is  an  ingenious 
method  adopted  by  one  manufacturer  to  reduce  the  amount 


Fig.  201 


Fig.  202 


Fig.  203 


Fig.  204 


Fig.  205 


of  platinum  (Fig.  206).  The  anchorage  is  in  the  form  of  a 
tube  embedded  in  the  porcelain,  the  inner  end  of  which  is 
expanded  into  a  flange  which  is  for  firm  retention.  The 
pins  of  alloy  are  made  to  fit  the  tubes  and  are  soldered  to 
them  with  high-grade  solder,  and  tests  seem  to  have  proved 
that  the  teeth  are  strong  enough  for  satisfactory  service. 

The  construction  of  teeth  whose  attachment  is  by  means 
of  an  undercut  recess  in  the  tooth  filled  with  the  plastic  base 
21 


322 


PORCELAIN  TEETH 


upon  which  they  are  mounted  is  another  attempt  to  reduce 
the  cost  of  production  by  doing  away  with  the  platinum 
entirely.  They  are  called  "pinless"  or  "diatoric  teeth." 
The  mechanical  difficulties  in  the  construction  of  a  tooth 
of  this  type,  which  shall  be  sufficiently  strong,  have  limited 


Fig.  206 


a,  base  metal  pin;  6,  platinum  anchorage;  c,  expanded  end  of  same. 

their  use  practically  to  the  bicuspids  and  molars,  in  which 
positions  under  favorable  conditions  they  are  eminently 
satisfactory.  It  must  be  remembered  that  as  their  strength 
depends  upon  the  bulk  of  porcelain  composing  them,  and 
that  as  this  is  less  than  in  pin  teeth,  it  is  not  possible  to  make 
more  than  minor  changes  in  them  by  grinding. 

Forms. — The  forms  of  porcelain  teeth  are  determined  by 
three  factors.  The  most  important  of  these  is  the  anatomical 
characteristics  of  the  teeth  they  are  to  substitute.  As  only 
the  crown  is  represented,  the  labial  or  buccal  surfaces,  the 
morsal  surfaces,  and  such  portions  of  the  approximal  surfaces 
as  are  presented  to  view,  are  patterned  after  the  natural 
teeth.  Teeth  quite  satisfactory  in  this  respect  are  manu- 
factured today,  although  the  market  contains  many  made 
according  to  old  designs  which  are  poor  imitations  of  the 
natural  organs.    The  form  of  the  incisors  and  cuspids  is  in 


CLASSIFICATION  OF  PORCELAIN  TEETH 


?23 


general  much  better  than  that  of  the  molars  and  bicuspids, 
the  occlusal  surfaces  of  many  of  which  are  too  narrow  for 
the  best  masticatory  results,  the  cusps  are  too  poorly  defined, 
and  no  attempt  is  made  to  have  those  of  opposing  sets  fit 
together. 

The  shape  of  the  other  portions  of  the  teeth  is  determined 
by  considerations  relative  to  their  attachment  to  the  base 
upon  which  they  are  mounted,  and  by  the  mechanical 
requirements  which  the  shape  and  relation  of  the  jaws 
impose.  Teeth  for  rubber  and  celluloid  work  are  similar 
in  design.     When  the  latter  came  into  use  the  artistic  pos- 


FiG.  207 


Fig.  208 


Fig.  209 


sibilities  of  the  new  material  created  a  demand  for  more 
natural  forms  in  teeth,  and  so-called  "celluloid"  teeth  were 
designed  to  meet  it.  Teeth  of  this  form  may  also  be  used 
with  a  cast  metal  ba.se,  but  thev  are  all  designated  rubber 
teeth. 

Plain  rubber  teeth  are  provided  with  two-headed  pins  to 
secure  their  attachment  to  the  vulcanite.  In  the  incisors  and 
cuspids  there  is  the  so-called  "pin  guard"  situated  between 
the  pins  and  the  morsal  edge  to  afford  a  shoulder  to  which 
the  vulcanite  may  be  finished.  The  "ridge  lap"  (Figs.  207, 
208,  and  209)  is  that  portion  of  the  tooth  which  comes  into 
relation  with  the  alveolar  ridge,  and  may  be  long  or  short 


324  PORCELAIN  TEETH 

in  accordance  with  the  requirement  of  the  case.  The  "bite," 
or  "overbite"  as  apphed  to  incisors  and  cuspids  is  that 
portion  of  the  tooth  intervening  between  the  pin  guard  and 
the  morsal  edge.  The  "shut  of  the  jaws"  refers  to  the  dis- 
tance between  the  jaws  when  the  mandible  is  in  the  proper 
position  for  the  occlusion  of  the  artificial  teeth.  Thus,  where 
the  distance  is  marked  we  have  a  "  long  shut,"  which  demands 
the  use  of  a  tooth  that  will  fill  in  the  space,  and  hence  is 
known  as  a  long-shut  tooth.  A  long-bite  tooth  would  fill 
in  the  space,  but  it  would  throw  too  much  strain  upon  the 
pins  to  remove  them  so  far  from  the  point  of  stress.  The 
bite,  shut,  and  ridge  lap,  it  will  be  seen,  are  all  correlated. 

Countersunk  pin  teeth  were  introduced  about  1885. 
Their  lingual  surface  corresponds  in  shape  to  that  of  the 
natural  teeth,  the  attachment  to  the  molded  base  being 
by  means  of  pins  located  in  a  depression  in  their  base.  Their 
close  conformity  in  contour  to  the  natural  organs  makes 
them  more  acceptable  to  the  tongue  than  teeth  backed  in 
the  ordinary  way,  and  renders  articulation  easier  and  more 
distinct. 

Inasmuch  as  they  must  be  mounted  almost  over  the 
alveolar  ridge,  they  cannot  be  used  in  cases  with  a  short  bite. 

For  a  vulcanite  base  the  case  should  be  flasked  in  the 
usual  way,  but  in  packing  each  countersink  should  be  care- 
fully filled  with  small  pieces  of  rubber  to  insure  the  rubber 
being  thoroughly  forced  into  the  countersink  and  around 
the  pins. 

Plain  plate  teeth  are  designed  for  use  on  a  metal  plate 
or  in  crown-and-bridge  work.  The  incisors  and  cuspids, 
in  either  instance,  are  similar  in  form,  but  those  for  use  in 
the  bicuspid  and  molar  region  for  crown-and-bridge  work 
represent  only  the  buccal  surface  of  the  tooth,  and  are  some- 
times known  as  "veneers." 

Continuous-gum  teeth  are  illustrated  in  Fig.  205.  It 
will  be  seen  that  they  have  only  one  long  pin,  and  that  the 
buccal  and  labial  portions  of  their  roots  are  represented  in 
porcelain.  This  contributes  to  the  firmness  of  their  attach- 
ment to  the  base,  the  porcelain  body  fusing  upon  the  roots 


CLASSIFICATION  OF  PORCELAIN  TEETH 


325 


and  uniting  them  to  the  plate.  It  also  maintains  the  con- 
tours of  these  regions  by  reducing  the  amount  of  porcelain 
body  to  be  baked,  and  hence  the  contraction  in  this  locality. 
Gum  Teeth. — Gum  teeth  are  made  for  metal  plates  and 
for  the  plastic  bases,  those  for  the  former  being  at  this  time 
made  only  as  single  teeth,  while  those  for  the  latter  are 
usually  in  sections  of  two  or  more  teeth  and  designated 


Fig    212 


Fig.   213 


Fig.   214 


Fig.  215 


"gum  section"  or  "block"  teeth  (Figs.  210  to  215).  The 
use  of  giun  teeth  is  limited  to  those  cases  in  which  resorption 
of  the  alveolar  process  has  taken  place  to  such  an  extent  as 
to  demand  considerable  restoration  by  means  of  the  denture. 
With  the  exception  of  that  found  in  continuous-gum  dentures 
the  {)orcelain  of  gum  teeth  provides  the  best  imitation  of  the 
natural  tissues  that  has  been  obtained,  but  the  fixedness  of 


326 


PORCELAIN  TEETH 


the  relation  between  the  teeth  in  the  section,  and  the  diffi- 
culty of  joining,  particularly  of  the  single  gum  teeth,  are 
drawbacks  which  this  does  not  overbalance.  The  artistic 
possibilities  in  arrangement  which  plain  teeth  offer  have 


Fig.  216 


Fig.  217 


caused  them  to  come  into  general  use,  and  in  most  cases  they 
are  to  be  preferred.  It  must  be  remembered,  however,  that 
in  some  full  dentures,  and  many  partial  ones,  gum  teeth  may 
be  used  to  great  advantage.  They  are  made  in  a  variety  of 
forms  and  offer  a  wide  selection. 


IMPROVEMENTS  IN  TOOTH  FORMS 

In  1907  Dr.  J.  Leon  Williams,  of  London,  England, 
started  a  campaign  in  the  dental  journals  for  better  tooth 
forms.  The  results  are  being  seen,  as  some  of  the  manufac- 
turers are  placing  upon  the  market  improved  forms  of 
bicuspids  and  molars. 

Dr.  Williams  found  it  was  no  easy  matter  to  induce  the 
manufacturers,  with  their  expensive  equipment  of  molds  and 
large  stock  of  artificial  teeth,  to  abandon  their  established 
methods,  though  unsatisfactory,  and  adopt  a  new  system 
based  upon  an  untried  theory.  However,  being  a  man  of  a 
highly  cultivated  artistic  temperament  and  much  deter- 
mination, he  resolved  that  the  time  was  ripe  for  the  much 
needed  improvements  in  artificial  teeth,  and  that  it  should 
be  brought  about. 

His  scheme  contemplates  the  standardizing  of  the  neces- 
sary stock  of  artificial  teeth.  (1)  By  selecting  the  typal 
forms  in  as  small  a  number  as  possible  to  meet  all  require- 


BASE  METAL  PINS  327 

ments.  This  he  finds  by  study  can  be  accompUshed  with 
twelve  typal  forms  and  three  sizes  of  each  form,  making 
thirty-six  molds.  (2)  The  artificial  teeth  to  be  accurate 
reproductions  in  size  and  form  of  natural  teeth  repre- 
sentative of  the  typal  form.  These  teeth  to  represent  the 
slightly  worn  condition  of  well-preserved  teeth  of  middle- 
aged  people.  (3)  That  each  of  the  classes  of  teeth,  as  vul- 
canite, metal  plate,  crown  and  bridge  facing,  and  crowns  shall 
be  duplicated  in  each  of  the  forms  and  sizes.  (4)  That  sample 
cases  shall  be  ecjuipped  with  blank  (without  pins)  teeth  of 
the  twelve  medium-sized  molds.  Thus,  the  practitioner  with 
his  twelve  sets  of  blank  teeth  will  have  a  guide  to  every 
tooth  the  system  contemplates.  Necessarily  considerable 
time  will  be  required  to  carve  the  model  teeth,  make  the 
molds,  and  manufacture  the  teeth  to  stock  the  market. 
However,  they  are  promised  for  the  near  future. 

BASE  METAL  PINS 

On  another  page  mention  has  been  made  of  the  use  of  base 
metal  as  a  substitute  for  platinum  in  the  pins  of  artificial  teeth. 
This  is  regretable  because  it  has  cheapened  the  product  far 
beyond  the  financial  saving.  In  fact,  it  is  questionable  if  the 
saving  in  production  justifies  the  dift'erence  in  the  selling  price; 
if  it  is  not  largely  sophistry  for  selling  the  product.  If  such 
debased  material  is  to  be  used  in  the  mouth,  it  can  logically  be 
used  only  with  cheap  work.  The  dentist  should  feel  that  to 
use  inferior  stock  in  high-grade  or  high-priced  work  is  an  impo- 
sition. The  blame  can  only  in  small  part  be  placed  upon  the 
manufacturer,  because  he  is  consistently  in  the  field  to  meet 
the  wants  of  the  profession;  although  his  enthusiasm  for 
trade  may  warp  his  judgment  and  color  his  statements.  The 
blame  is  largely  to  the  discredit  of  the  dentist,  because  his 
only  motive  can  be  no  more  than  the  .saving  of  a  few  pennies 
on  a  set  of  teeth,  for  which  he  risks  his  reputation  and  brings 
reproach  upon  his  profession.  The  profession  should  demand 
(A  the  dental  trade  the  best  only  that  science  and  art  can 
produce.  The  lowering  of  the  standard  of  quality  should 
in  no  wise  be  encouraged. 


CHAPTER    IX 

DOUBLE  VULCANIZATION  METHOD 

In  the  preceding  chapters  the  underlying  principles, 
the  nature  and  the  requirements  for  artificial  dentures  has 
been  discussed.  Chapter  VI  treats  of  the  history,  appli- 
ances, and  primitive  method  of  vulcanite  construction,  while 
this  chapter  presents  an  advanced  technique  of  construction. 
By  double  vulcanization  is  meant  that  a  vulcanite  base- 
plate is  made,  and  to  it  the  superstructure  is  added  at  a 
second  vulcanization.  The  advantages  of  this  method  over 
the  single  vulcanization  method  is  that  it  provides  a  perfect 
fitting  base-plate,  provided  the  impression  was  a  good  one; 
and  it  very  much  facilitates  the  developing  of  the  esthetics 
or  cosmetic  effects  of  the  artificial  denture. 


TECHNIQUE 

The  method  consists  of  taking  the  impression,  making  the 
cast,  forming  the  base-plate,  obtaining  the  occlusion  and 
contour  models,  arranging  the  teeth,  and  proving  the  contour 
and  expression;  of  preparing  the  case  for  flashing,  packing, 
vulcanizing,  and  finishing. 

Impressions. — It  is  imperative  in  this  as  in  all  kinds  of 
artificial  dentures  that  a  perfect  plaster  impression  be 
obtained.  The  technique  of  this  operation  is  described  in 
Chapter  II. 

Cast. — Because  of  the  heavy  pressure  to  which  the  cast 
will  be  subjected  in  molding  the  rubber,  it  should  be  made 
of  a  material  that  cannot  be  easily  compressed.  Spence 
plaster  compound  is  best  for  this  purpose  (see  Chapter  III). 
Additions  are  made  to  the  cast  either  in  the  form  of  a  relief 
or  as  a  vacuum  chamber  (see  Chapter  VII). 


TECHNIQUE  329 

Base-plate. — The  vulcanite  base-plate  is  constructed  as 
described  on  page  132.  The  base-plate  should  be  con- 
structed of  the  purest  rubber,  as  Dougherty's  pure  black 
rubber,  Traun's  uncolored  rubber,  or  Ash's  dark  elastic 
rubber. 

Occlusion  and  Contour  Models. — The  occlusion  and  contour 
models  are  constructed  as  described  on  page  133.  The 
models  are  mounted  on  the  New  Century  Antagonizor  by 
aid  of  the  Snow  face  bow  (Fig.  98). 

Mounting  the  Teeth. — The  teeth  are  mounted  as  directed 
in  Chapter  \l  (Fig.  218).  The  patient  is  about  sixty  years 
of  age  and  of  the  sanguine  modified  by  the  nervous  temper- 

FiG.  218 


ament.  The  teeth  selected  for  the  case  were  S.  S.  W.  "  nat- 
ural forms,"  mold  No.  227,  Shade  No.  40.  It  will  be  observed 
that  the  teeth  are  of  sufficient  length  to  nearly  fill  the  space 
between  the  high  and  low  lip  lines,  so  that  when  the  lips 
are  parted  to  their  farthest,  only  a  slight  trace  of  gum 
restoration  will  be  observable— so  slight,  indeed  that  the 
material  should  not  be  noticeable. 

The  overlap  may  be  seen  in  Fig.  218.    The  lateral  inch- 


330 


DOUBLE   VULCANIZATION  METHOD 


nation,  compensating  curve,  and  diverging  straight  line  are 
shown  in  Fig.  219.  The  esthetic  .features  may  be  studied 
in  Figs.  218  and  219. 


Proving  the  Contour  and  Expression. — This  phase  of  the 
subject  is  discussed  in  Chapter  XVI. 

Preparation  of  the  Case  for  Flasking. — Strings  are  used  for 
outhning  the  festoons  and  periphery  of  the  gum.  The  object 
of  the  festooning  string  at  the  cervical  portion  of  the  teeth 
is  to  give  the  proper  thickness  to  the  margin  of  the  gum. 
The  string  used  for  this  purpose  is  waxed  dental  floss, 
twisted  very  hard,  doubled,  and  twisted  again.  In  doubling, 
the  loop  will  show  the  direction  it  should  be  twisted  the 
second  time.  Wax  the  string  well  with  softened  wax  and 
apply  it  by  grasping  the  left  heel  of  the  plate  between  the 
fingers  and  thumb  of  the  left  hand,  with  the  occlusal  surface 
of  the  teeth  upward;  place  one  end  of  the  string  at  the  distal 
surface  of  the  second  molar,  pressing  it  gently  into  the  wax; 
outline  the  margin  of  the  gum,  using  the  wax  spatula  to 
carry  the  string  well  into  the  interproximal  spaces.  The 
peripheral  string  should  be  well-waxed  wrapping  twine, 
placed  at  the  outer  edge  of  the  wax,  and  secured  in  place 


TECHNIQUE  331 

by  melted  wax  made  smooth  with  a  hot  spatula.  Fig.  220 
illustrates  the  usual  manner  of  applying  the  strings.  The 
peripheral  string  should  l)e  applied  at  the  line  of  separation 
of  the  flask,  and  this  must  be,  in  cases  of  heavy  restorations, 
at  the  widest  portion  of  the  wax  model. 

Fig.  220 


The  next  step  is  to  cover  the  buccal  and  labial  surfaces 
with  a  strip  of  5so.  GO  tinfoil.  Instructions  are  necessary  in 
applying  the  tin  over  the  strings.  The  No.  3  instrument  of 
the  Evans  set  of  carvers  (Fig.  104)  is  especially  adapted  for 
adjusting  the   tinfoil.     The  strip  of  foil  is  placed  over  the 


Fia.  221 


wax  and  teeth  and  pressed  as  closely  as  possible  with  the 
fingers.  The  surplus  tin  is  cut  away  with  fine-pointed 
scissors.  Two  pairs  are  desirable,  one  straight  and  the 
other  curved.  The  erlge  of  the  tin  may  be  anywhere  between 
the  morsal  ends  and  the  middle  of  the  teeth.  The  tin  should 
be  slit  between  each  two  teeth.     Fig.  221  shows  the  tin 


332  DOUBLE  VULCANIZATION  METHOD 

trimmed  and  slitted.  Hold  the  work  in  the  left  hand,  seize 
the  instrument  by  the  hand  grasp,  rest  the  thumb  upon  the 
occlusal  surface  of  the  second  molar,  and  burnish  the  tin 
closely  to  the  tooth  and  against  the  festoon  string.  Continue 
this  operation  with  all  the  teeth.  After  adjusting  the  tin 
about  the  teeth,  the  metal  must  be  burnished  over  the 
string  to  give  the  desired  thickness  of  the  gum  and  the 
contour  of  the  festoon.  This  is  done  by  holding  the  plate 
and  burnisher  in  the  same  manner  as  before.  The  instrument 
must  extend  one-sixteenth  of  an  inch  beyond  the  string  and 
at  the  same  time  must  rest  upon  the  body  of  the  tooth  while 
pressing  the  tin  down  over  the  festoon  string.  By  this 
means  a  proper  thickness  and  contour  is  given  the  margin 
of  the  gum,  without  forming  an  unnatural  beaded  edge. 
After  all  the  teeth  have  been  thus  treated,  the  position  of 
the  plate  should  be  reversed  in  the  left  hand,  so  that  the 
thumb  of  the  right  hand  may  rest  upon  the  periphery  of 
the  base-plate  while  burnishing  the  tin  from  the  festoons 
toward  the  periphery.  With  a  pair  of  sharp  curved  scissors 
trim  the  tin  flush  with  the  peripheral  string,  but  do  not 
permit  it  to  overlap  the  vulcanite  base-plate.  The  case  is 
now  ready  for  tinning  the  lingual  surface.  Use  No.  60  foil, 
and  if  the  vault  is  a  high  one,  slit  the  tin  from  the  middle 
of  one  side  to  the  centre.  Place  the  inner  end  of  the  slit 
over  the  middle  of  the  vault,  and  one  edge  of  the  slit  along 
the  raphe  to  the  palatal  border;  press  the  side  of  the  foil 
gently  against  the  wax  and  teeth;  press  the  other  half  of 
the  tin,  in  the  same  manner,  into  position,  permitting  the 
slit  portion  to  overlap  the  first  half.  With  sharp  scissors 
trim  the  tin  nearly  down  to  the  teeth.  Remove  the  foil 
and  place  it  upon  a  plaster  or  metal  cast  having  well-defined 
rugse,  and  burnish  the  rugse  into  the  foil.  Remove  the  foil, 
turn  it  over,  and  fill  the  impressions  of  the  rugse  with  wax, 
also  smear  the  remainder  of  this  surface  with  a  thin  layer  of 
wax;  now  replace  the  waxed  surface  agaiast  the  vault  of  the 
plate  and  nicely  adjust  with  the  fingers.  The  tin  must  be 
securely  burnished  against  the  teeth.  The  lingual  contour 
of  the  teeth  is  produced  by  roughly  carving  away  the  excess 


TECHNIQUE 


333 


of  wax,  with  the  Evans  wax  carvers,  just  before  placing  the 
tin.  The  tin  is  also  slit  between  the  teeth  on  their  lingual 
aspect  and  nicely  burnished  to  place  (Fig.  222). 


Fig.  222 


^ki 


Flasking. — A  flask  with  a  narrow  rim  is  imperative.  The 
star  flask,  as  shown  in  the  following  illustrations,  will  do 
very  well,  but  one  made  b>-  the  Cleveland  Dental  Manu- 
facturing Co.,  called  the  Wilson  flask  (Fig.  108),  will  better 
serve  the  purpose.  This  flask  is  designed  to  be  used  with  the 
Donham  clamp  (P'ig.  109 j. 


Fig.  223 


The  maxillary  surface  of  the  case,  having  l)een  cleaned  of 
wax,  is  filled  with  S[)ciicc's  c(>mi)(>utid,  which  forms  a  cast 
upon  which  the  denture  is  vulcanized.  This  yulcanizaticm 
cast  should  be  not  less  than  one-fourth  of  an  inch  thick  at 


334 


DOUBLE   VULCANIZATION  METHOD 


the  thinnest  portion  of  the  vault,  and  should  not  overlap 
the  tin  facing.  In  one  hour  this  cast  will  be  sufficiently 
hard  to  place  in  the  first  section  of  the  flask  with  regular 
dental  plaster  (Fig.  223).  The  peripheral  string  will  be  a 
great  aid  in  outlining  the  denture  in  the  flasking  plaster. 
After  the  plaster  has  set,  it  is  coated  with  a  separating  fluid, 
and  then  held  under  the  faucet  so  as  to  moisten  the  tinfoil 
and  thus  facilitate  the  flowing  of  plaster  into  the  interproxi- 
mal spaces  at  the  time  the  flasking  is  completed.  The  flask 
should  stand  about  thirty  minutes  and  then  be  placed  over 
the  stove  in  a  stew-pan  of  cold  water,  to  be  heated  up  as  before 
described  on  page  251. 

Fig.  224 


Separating  the  Flask. — When  the  heat  of  the  water  indi- 
cates the  time  for  opening,  the  flask  is  grasped  with  a  cloth 
holder  in  the  left  hand  and  separated  by  the  point  of  a  knife- 
blade  or  wax  spatula  inserted  at  the  heel  of  the  flask.  The 
instrument  should  be  guarded  by  the  thumb  and  finger  of 
the  right  hand  to  avoid  the  possibility  of  marring  the  case. 


TECHNIQUE 


^35 


The  strings  and  as  much  of  the  wax  as  possible  are  removed 
with  the  spatula,  after  which  the  remainder  is  removed  by 
pouring  boiling  water  upon  it;  then  with  a  cloth  the  tin  lin- 
ing and  vulcanite  base-plate  are  wiped  dry  (Figs.  224  and 
225).  The  excess  space  is  cut  with  small  gate  connections 
(Fig.  225),  and  the  separated  flask  is  placed  over  the  sheet- 
iron  to  warm  as  previously  described  (Chapter  VI,  Fig  156). 


Fig.  225 


S^\^ 


Packing. — Sufficient  Gilbert  Walker's  granular  gum  or 
pink  rubber  is  cut  into  strips  to  form  a  layer  of  one 
thickness  over  the  tinned  surface.  First  pack  a  narrow  strip 
of  red  rubber  about  the  pins  (Fig.  226,  c),  and  small  square 
or  triangular  pieces  of  granular  gum  between  the  cervical 
portions  of  the  teeth.  The  .stri])s  of  granular  gum  are  then 
placed  over  the  labial  and  buccal  surfaces  of  the  matrix 
with  the  fingers  and  wax  spatula  so  that  no  space  remains 
through  which  the  red  rubber  can  escape.    The  strip  of  red 


336 


DOUBLE  VULCANIZATION  METHOD 


rubber  about  the  pins  should  be  pressed  down  with  a  wax 
spatula  to  form  a  symmetrical  outline.  A  piece  forming 
a  half -circle  of  granular  gum  is  then  placed  over  the  anterior 
portion  of  the  lingual  surface  (Fig.  226,  a),  and  with  the  wax 
spatula  the  circular  edge  is  joined  to  the  red  rubber  about  the 
pins  of  the  teeth.  A  piece  sufficiently  large  when  stretched 
to  half  its  thickness  (Fig.  226,  h),  is  then  applied  over  the 
remaining  portion  of  the  lingual  surface,  and  its  edges  are 


united  to  the  contiguous  rubber.  Strips  of  red  rubber  are 
then  placed  over  the  teeth  to  nearly,  but  not  quite,  fill 
the  mold.  A  separating  cloth  of  closely  woven  cotton,  or 
the  cloth  removed  from  the  rubber  after  the  sizing  has  been 
washed  out,  is  saturated  with  warm  water  and  placed  over 
the  rubber  in  the  mold,  when  the  two  sections  of  the  flask  are 
placed  together.  If  the  packing  has  been  expeditiously 
done  and  the  rubber  is  sufficiently  warm,  it  is  placed  in  the 


TECHNIQUE  337 

flask  press  and  gentle  pressure  applied.  The  flowing  of  the 
rubber  should  be  followed  every  ten  seconds  with  a  partial 
turn  of  the  screw  until  the  flask  is  closed.  The  flask  is  then 
removed  from  the  press  and  .separated.  If  there  is  not 
an  excess  of  rubber,  the  cloth  will  easily  separate  from  the 
rubber,  but  should  there  be  strong  adhesion,  saturation  of 
the  cloth  with  water  will  facilitate  its  removal.  Attention 
is  again  called  to  the  danger  of  warping  the  denture  while 
closing  the  flask.  This  is  especially  so  with  the  double 
vulcanization  method  because  of  the  small  amount  of  rubber 
required  to  cover  the  lingual  surface  (see  Chapter  VI). 

Vulcanizing. — The  case  is  vulcanized  in  the  same  manner 
as  the  base-plate.  Preference  is  given  to  low  temperature 
and  long  time,  300°  Y.,  for  three  hours  from  the  time  of 
applying  the  heat.  It  should  not  be  taken  from  the  flask 
until  cold  (see  Chapter  VI). 

Fig.  227 


Finishing. — After  washing  to  remove  the  loose  plaster,  the 
tin  may  be  easily  stripped  oft",  and  the  excess  vulcanite  flled 
from  the  periphery  of  the  denture.  A  sharp  chisel  should 
be  used  to  trim  about  the  labial  and  buccal  surfaces  of  the 
teeth,  but  the  lingual  surface  should  be  trimmed  with  a 
scraper.  The  file  marks  about  the  periphery  of  the  plate 
should  be  removed  with  fine  sandpaper.  The  labial,  buccal, 
and  lingual  surfaces  are  buft'ed  with  felt  wheels  and  cones 
22 


338 


DOUBLE  VULCANIZATION  METHOD 


carrying  pulverized  pumice  and  water.  The  spaces  between 
the  teeth  are  best  reached  with  a  stiff  bristle  brush  wheel, 
using  wet  pumice.  All  the  surfaces,  including  the  maxillary, 
are  glossed  by  using  a  rapidly  revolving  soft  brush  wheel 
and  whiting  wet  with  alcohol  or  water. 


Fig.  228 


Fig.  229 


Illustrations. — P'ig.  227  is  the  completed  case  shown  in 
occlusion.  Fig.  228  presents  the  lingual  aspect  of  the  teeth 
and  the  reproduced  rugse.  Fig.  229  shows  the  maxillary  and 
mandibular  surfaces. 

Conclusion. — ^The  double  vulcanization  method  is  best 
adapted  to  full  cases,  but  may  be  used  in  partial  cases.  The 
tin  finishing  method  is  applicable  to  the  single  vulcanization 
method  as  well  as  to  the  double.  It  is  the  easiest  and  best 
method  of  forming  the  contour  of  the  surfaces  of  the  denture; 
also  producing  a  dense  surface  on  the  vulcanite. 


CHAPTER    X 

ALUMINUM  BASE-PLATE 

History. — Aluminum  was  known  theoretically  long  before 
it  was  reduced  to  a  pure  metal.  In  the  early  part  of  the 
nineteenth  century  Sir  Humphry  Davy  named  the  metal 
"alumium,"  signifying  that  it  is  the  metal  of  alum.  Other 
scientists  contended  that  the  metal  should  be  named  from 
its  oxide  alumina,  therefore  aluminium.  In  1812  Davy 
compromised  and  called  it  aluminum,  which  name  is  the 
generally  accepted  one  of  today. 

Wohler  was  the  first  to  reduce  it  to  a  metal  in  1827. 
Deville  took  it  from  the  rank  of  a  curiosity  and  made  it  one  of 
the  useful  metals  in  1854.  Deville's  process  of  manufacture 
was  known  as  the  sodium  process.  August  18,  1885,  E.  H. 
and  A.  H.  Cowles,  of  Cleveland,  recei\ed  a  patent  for  an 
electrical  process  for  making  aluminum  alloys.  In  1886 
Charles  M.  Hall,  of  Oberlin,  Ohio,  applied  for  a  patent, 
which  was  granted  April,  1889.  This  process  produced  pure 
aluminum  by  electrolysis.  This  process  is  used  by  the  Alumi- 
num Company  of  America,  whose  principal  plant  is  located 
at  Niagara  Falls.  In  1855  the  metal  was  worth  nearly  $10U 
a  pound;  today  the  purest  metal  on  the  market  can  be 
purchased,  in  quantity,  at  less  than  thirty  cents  a  pound. 

Physical  and  Chemical  Properties. — Aluminum  is  a  silvery 
white  metal.  Its  specific  gravity  is  2.50.  It  fuses  at  657°  C. 
or  1215°  F.  Its  specific  heat  is  high.  Its  lineal  expansion  is 
relatively  high;  of  the  common  metals  it  is  only  exceeded 
by  zinc  and  lead.  As  a  thermal  conductor  it  is  better  to 
compare  it  with  the;  other  metals.  Ag,  100;  (!u,  7.'^. 6;  Au, 
53.2;  Al,  31.3;  Zn,  28.1;  Sn,  15.2;  Pb,  8.5;  Pt,  8.4.  Pure 
alumirmm  has  go(xl  tensile  strength;  but  is  not  very  rigid; 
it  will  bend  nearly  double.     It  is  about  as  hard  as  copper; 


340  ALUMINUM  BASE-PLATE 

it  is  just  below  copper  in  ductility,  and  nearly  as  malleable 
as  gold.  Aluminum  powder  is  the  ground  leaf.  It  is  electro- 
positive to  all  other  metals  used  in  the  mouth,  therefore  it  is 
the  one  that  would  be  destroyed  if  a  voltaic  couple  is  formed. 
This  property  and  its  lack  of  rigidity  unfits  it  for  partial 
dentures.  The  impurities  of  aluminum  are  iron  and  silicon. 
The  Aluminum  Company  of  America  gives  the  composition 
of  their  No.  1  grade  as:  Silicon,  0.30;  iron,  0.15;  aluminum, 
99.55  per  cent.  This  grade  is  usually  99.25  to  99.40  per  cent, 
pure.  Their  No.  2  grade  contains  2  per  cent,  each  of  iron 
and  silicon.  The  natural  solvent  for  aluminum  is  hydro- 
chloric acid,  the  other  mineral  acids  having  little  or  no 
action.  Sulphur  at  less  than  a  red  heat  does  not  act  upon  it. 
Solutions  of  caustic  alkalies,  chlorine,  bromine,  iodine,  and 
hydrofluoric  acid  act  readily  and  corrode  the  metal.  It 
withstands  the  action  of  organic  secretions  better  than  does 
silver.  Therefore,  it  is  used  for  dental  plates,  for  surgical 
instruments,  and  for  articles  subjected  to  carbolic  acid  or 
other  organic  antiseptic  solutions;  but  antiseptic  solutions 
of  mineral  salts  should  not  be  used  upon  it.  It  is  not  injured 
by  the  salt  and  vinegar  used  for  culinary  purposes. 

Aluminum  Base-plate. — Aluminum  is  used  as  a  base-plate 
both  by  the  casting  and  swaging  methods.  It  was  first  used 
for  the  casting  method  by  Dr.  J.  B.  Bean  of  Baltimore.  He 
cast  it  under  pressure  of  a  column  of  the  metal  several  inches 
high.  Dr.  C.  C.  Carroll,  of  Ravenna,  Ohio,  later  of  Mead- 
ville.  Pa.,  and  New  York  City,  developed  a  process  of  casting 
aluminum  under  air  pressure,  using  a  rubber  bulb.  Dr.  R.  C. 
Brophy,  of  Chicago,  invented  a  method  and  process  for 
casting  by  jarring  the  molten  metal  into  the  mold.  All  of 
these  inventors  used  alloys  of  aluminum,  deeming  it  impos- 
sible to  make  dental  castings  of  pure  aluminum.  Carroll's 
alloy,  as  given  by  Goddard,  was  Al,  98  parts;  Pt,  Ag,  and  Cu, 
2  parts.  Richards  states  that  Carroll's  alloy  consisted  of 
Al,  90  to  93  parts;  Ag,  5  to  9  parts;  and  Cu,  1  part.  Brophy's 
Aerdentalloy  consists  of  Al,  90  parts,  and  Ag  and  Sn,  10 
parts. 

The  writer  believes  that  the  first  successful  castings  of 


INYESTMEXT  COMPOUND  CAST  341 

pure  aluminum  for  artificial  dentures  were  made  subsequent 
to  Dr.  Taggart  announcing  his  method  of  casting  gold  in 
January,  1907.  Early  in  1908  Dr.  D.  D.  Campbell,  of 
Kansas  City,  Mo.,  presented  the  "cow  bell"  (centrifugal) 
method  in  the  Dental  Brief,  and  Dr.  J.  H.  Billmeyer  of, 
Norwalk,  Ohio,  presented  his  methods  in  the  Dental  Svmmary 
and  Dentist's  Magazine.  This  method  is  luidoubtedly  the 
most  successful  method  yet  devised  for  casting  pure  alumi- 
num. It  uses  the  bucket  and  centrifugal  force  method,  but 
its  essential  and  new  (to  dentistry)  principle  is  ha\'ing  the 
feed  sprue  enter  at  the  bottom,  and  the  vent  sprues  at  the 
highest  points  of  the  mold.  The  vacuum  principle  is  also 
used  for  casting  pure  aluminum,  as  exemplified  in  the  Elgin 
Vacuum  Machine. 

Technique. — The  technique  of  making  a  pure  aluminum 
casting,  based  upon  the  Billmeyer  method,  consists  of  a 
properly  taken  plaster  impression,  investment  compound 
cast,  wax  model,  flasking,  heating,  melting  of  metal,  casting 
and  finishing. 

Impression  taking  is  described  in  Chapter  II. 

Investment  Compound  Cast. — The  impression  is  coated  with 
shellac  varnish  and  glossed  with  sandarac  varnish.  It  is 
filled  with  any  good  non-shrinking  investment  compound. 
An  excellent  material  consists  of  silica  sand  (white  lake 
.sand),  wash  or  float  silica,  and  plaster  of  Paris,  equal 
parts  by  measure.  Silica  is  the  highest  fusing,  the  least 
expanding  and  contracting,  and  the  best  conductor  of  heat 
of  any  material  at  command.  It  is  coarse  and  forms  centres 
toward  which  the  shrinkage  of  the  bond  material  ma\'  draw, 
thus  preventing  warpage  and  cracking  of  the  mass  of  material. 
The  fine  sihca  fills  the  pores,  and  the  plaster  serves  only  as 
a  l)ond;  therefore  the  strength  of  the  compound  will  depend 
upon  the  quality  of  the  bond.  As  a  slow-.setting  plaster 
is  stronger  than  a  quick-setting  one,  it  is  evident  that  the 
poorer  grades  of  plaster  will  make  the  stronger  investment 
comi)Ound,  l)ut  slow  setting,  and  vice  versa.  The  ingredients 
of  the  compound  are  thoroughly  mixed  })y  passing  five  times 
through  a  sieve. 


342  ALUMINUM  BASE-PLATE 

It  will  require  3^  to  4  parts  of  this  compound  to  1  part 
of  water,  by  measure,  to  make  a  suitable  mix  for  filling  an 
impression.  While  filling  the  impression  the  material  must 
be  thoroughly  jarred  into  place,  thereby  producing  a  smooth 
surface  upon  the  cast. 

The  relief  or  vacuum  chamber  may  be  produced  by  either 
of  two  methods— (1)  carving  the  impression,  or  (2)  adding 
to  the  cast.  If  the  addition  method  is  chosen,  a  thin  solu- 
tion of  a  fine  grain  investment  compound  is  painted  onto 
the  cast.  To  be  assured  that  the  added  portion  is  thor- 
oughly attached,  the  cast  is  well  saturated  with  water  over 
the  portion  to  which  the  addition  is  to  be  made.  A  good 
formula  for  a  fine-grained  investment  compound  is  two  or 
three  parts  by  measure  of  wash  silica  and  one  part  of  plaster, 
thoroughly  mixed  by  sieving. 

Wax  Model  Base-plate. — The  object  sought  in  forming  the 
wax  model  for  a  cast  aluminum  base-plate  is  to  so  place  the 
material  that  the  finished  product  shall  have  at  every  part 
sufficient  body  to  resist  the  stress  to  be  placed  upon  it;  to 
form  square  joints,  thus  no  feathery  edge  of  either  vulcanite 
or  metal;  and  to  provide  for  securely  attaching  the  teeth  by 
means  of  vulcanite  to  the  base-plate. 

Technique. — A  sheet  of  pink  base-plate  wax  is  warmed  and 
evenly  adjusted  to  the  cast,  the  excess  is  cut  away  with  a 
warmed  wax  knife  and  the  edges  luted  to  the  cast.  It  is 
evident  that  the  thickness  of  the  sheet  of  base-plate  wax 
will  control  the  thickness  of  the  casting,  therefore  a  wax  of 
suitable  thickness  to  produce  the  desired  result  must  be 
used.  The  additions  to  the  wax  base-plate  are  made  by  the 
use  of  rolls  of  pure  yellow  beeswax.  These  rolls  are  made  by 
cutting  a  strip  of  impression  wax,  one-fourth  of  an  inch  wide, 
warming  it  in  the  flame,  and  working  it  with  the  fingers  until 
it  is  evenly  soft  and  in  the  form  of  a  roll.  It  is  placed  upon  a 
clean  flat  surface  (top  of  the  work  bench  is  excellent),  and 
rolled  under  pressure  with  another  flat  surface  (a  slab  of 
glass  T  by  3  by  6  inches  is  desirable) .  This  first  strip  of  wax 
should  be  reduced  by  rolling  to  \  of  an  inch  in  diameter. 
The  roll  is  warmed  slightly  and  conformed  by  the  fingers  to 


TECHNIQUE 


343 


the  buccal  and  labial  borders  of  the  wax  base-plate;  the  roll 
is  continued  to  outline  the  lingual  portion  of  the  alveolar 
process.  Necessarily  judgment  must  be  exercised  in  placing 
the  roll  of  wax  so  that  its  substance  will  give  the  desired 


Fig.  230 


Fio.  231 


contour  to  the  nio<h-l  base-plate.  Fig.  I'MO  shows  the  i)nik 
base-plate  wax  adjusted  and  the  peri[)h(ral  wax  as  acljnsted 
by  the  fingers.  The  roll  of  wax  is  contoured  and  united  to 
the  base-plate  by  using  a  hot  ironing  spatula.    Fig.  231  shows 


344  ALUMINUM  BASE-PLATE 

the  wax  roll  so  manipulated  that  it  presents  a  square  ledge 
against  which  the  vulcanite  attachment  will  rest  in  the 
finished  denture.  The  next  step  in  forming  the  wax  model 
is  to  make  provision  for  securely  holding  the  vulcanite 
attachment  to  the  metal  casting.  This  is  best  done  by  means 
of  a  row  of  cleats  as  near  the  edge  of  vulcanite  and  casting 
as  it  is  possible  to  place  them.  These  cleats  are  formed  of 
wax  rolled  to  a  diameter  of  yV  of  an  inch,  or  less,  and 
bent  into  a  series  of  loops.  This  looped  roll  is  placed 
upon  the  model  base-plate  and  the  points  of  contact  luted 
by  a  touch  of  a  hot  wax  spatula.     When  the  wax  is  cold 

Fig.  232 


the  tops  of  the  loops  are  cut  away  with  a  pair  of  small  curved 
scissors.  Fig.  232  illustrates  the  attached  loops  upon  one 
side  of  the  wax  model  and  the  cleats  as  formed  by  shearing 
upon  the  other  side. 

The  completed  wax  model  plate  is  prepared  for  flasking 
by  attaching  gate  or  sprue  formers.  These  are  one  feed  or 
pouring  sprue  and  two  vent  sprues.  The  feed  sprue  former  is 
a  roll  of  yellow  wax,  which  must  not  exceed  y^  of  an  inch  in 
diameter,  attached  near  the  lowest  part  of  the  wax  model  as 
it  is  to  stand  in  the  flask.  It  is  obvious  that  the  larger  the 
feed  sprue  hole  the  more  quickly  the  mold  may  be  filled  with 
the  molten  metal ;  and  the  smaller  the  sprue  hole  the  more 


TECHNIQUE 


345 


clanger  of  an  incomplete  casting  from  the  metal  chilling.  How- 
ever, as  the  feed  sprue  hole  connects  with  the  bottom  of  the 
melting  crucible,  there  is  a  limit  to  its  size.  This  limit  of 
safety  has  been  found  by  practice  to  be  fV  o^  ^^  inch.  A 
sprue  of  I  inch  diameter  is  almost  certain  to  permit  the  first 
molten  metal  to  fall  into  and  clog  the  lower  end  of  the  hole, 


Fig.  233 


Fig.  234 


thereby  preventing  the  filling  of  the  mold.  The  explanation 
of  this  fact  is  that  the  specific  gravity  of  the  metal  resting 
over  a  |^-inch  diameter  hole  is  greater  than  the  cohesion  of 
tlie  molten  metal.  The  vent  sprue  formers  are  14  or  16  B. 
and  S.  gauge  iron  wire  attached  to  the  highest  points  of 
the  wax  models.      Fig.  2'X\  shows  the  sprues  jjroj)crly  attached 


346 


ALUMINUM  BASE-PLATE 


to  the  upper  wax  model  base-plate.  Fig.  234  shows  the 
Billmeyer  casting  bucket  or  flask  of  sheet  iron,  with  the 
handle  attached.  Fig.  235  is  a  diagram  of  the  flask,  model 
base-plate,  sprue  formers,  and  melting  crucible. 


Fig.  235 


d      h 


Flasking. — There  are  two  steps  to  the  flasking  procedure — 
(1)  investing  the  wax  model  base-plate,  and  (2)  flasking  the 
invested  case. 

The  wax  model  base-plate  securely  luted  to  the  cast  is 
covered  with  water  while  making  a  thin  batter  of  investment 
compound,  using  the  same  material  of  which  the  cast  was  made. 
The  cast  and  model  are  removed  from  its  bath  and  excess 
moisture  quickly  absorbed  with  a  napkin.     The  investment 


FLASKING 


347 


batter  is  applied  to  the  wax  model  with  a  }-inoh  ox-hair  paint 
brush.  Fig.  230  shows  the  case  invested.  If  the  investment 
compound  is  made  of  slow-setting  plaster,  the  invested  piece 
should  stand  about  ten  minutes;  but  if  the  investment  is 
quick  setting,  the  second  step  may  proceed.  This  will  require 
a  plaster  bowlful  of  the  investment  compound  of  a  little  stiff er 
consistency  than  that  applied  with  a  brush.    The  material  is 


Fig.  236 


all  placed  in  the  flask,  and  the  invested  case  pressed  well 
down  toward  the  bottom  of  the  flask,  at  the  same  time 
rapping  the  flask  on  the  bench  to  assure  the  jjcrfect  adap- 
tation of  the  second  investment.  When  the  investment  is 
partially  set  a  cavity  is  carved  about  the  wax  casting  sprue 
former  for  the  melting  crucible.  This  is  shown  in  Figs.  235 
and  237.     When  the  investment  compound  has  thoroughly 


348 


ALUMINUM  BASE-PLATE 


Fia.  237 

k;. 

c 

mm' 

(kY. 

^ 

fll 

ikL 

§ 

:£ 

Fig.  238 


CAUTION  349 

set  the  inside  of  the  crucible  mold  is  scraped  smooth  with  a 
romid-end  \iilcanite  scraper.  This  will  leave  the  wax  sprue 
former  just  flush  with  the  floor  of  the  crucible.  All  particles 
of  loose  compound  must  be  brushed  or  jarred  out.  The  flask 
case  is  placed  in  a  warm  place  (not  in  an  open  flame)  to  dry 
and  soften  the  wax;  as  soon  as  the  wax  begins  to  rini,  the 
vent  sprue  wires  are  drawn  and  the  case  inverted  upon  the 
gas  stove  (Fig.  238).  As  the  wax  of  the  model  melts,  it  either 
ignites  or  drops  upon  the  bench.  There  should  be  no  smudge 
of  burning  wax  if  it  is  in  direct  contact  with  the  flame,  as  the 
carbon,  hydrogen,  and  oxygen  are  so  proportioned  in  wax 
that  it  burns  smokeless  under  favorable  conditions.  For  the 
first  ten  or  fifteen  minutes  the  gas  is  turned  on  about  one-half, 
and  then  for  the  rest  of  the  heating  up  it  is  on  full.  The  flask 
should  be  heated  in  the  inverted  position  for  one  hour  or 
until  there  is  no  flame  issuing  from  the  feed  sprue  hole,  thus 
signifying  that  the  wax  is  completely  burned.  The  flask  is 
reversed,  that  is,  the  small  end  is  down  for  half  an  hour. 
Heating  for  another  half  hour  will  do  no  harm,  but  it  is 
unnecessary. 

The  No.  1  aluminum  is  purchased  in  bars  described  as 
small  notched  bars  (s.  n.  b.)  containing  about  one  and  one- 
half  pounds  of  metal,  notched  into  six  sections.  Each  section 
may  be  cut  into  three  pieces  of  about  equal  size.  One  of  these 
small  pieces  will  suffice  for  any  ordinary  casting.  The  metal  is 
very  tough,  therefore  hard  to  cut.  The  author  cuts  it  upon 
the  swaging  block  with  a  cold  chisel  and  heavy  swaging 
hammer.    The  cutting  is  no  light  task. 

Caution. — Alumiiuim  is  considered  a  connecting  link  be- 
tween the  noble  and  base  metals,  nevertheless  it  is  l)ase  and 
has  the  property  of  absorbing  its  oxides,  also,  markedly,  the 
property  of  occluding  gases.  This  latter  property  is  evi- 
denced by  the  odor  of  garlic  (carbon  compound),  often 
noticeable  in  a  newly  made  casting,  also  the  lack  of  uniform 
density  shown  h)y  burnishing  a  buffed  surface  of  the  metal. 
This  implies  that  aluminum  that  has  once  been  melted  in  a 
dental  laboratory  should  be  discarded.  Upon  the  second  or 
third  melting  of  the  metal  a  yellowish  tinge  may  be  noticed; 


350  ALUMINUM  BASE-PLATE 

this  indicates  superficial  oxidation.  Should  the  color  appear 
with  the  first  melting  of  the  metal,  it  would  indicate  that 
the  metal  has  been  overheated,  and  that  the  casting,  to  that 
extent,  is  defective. 

Melting  the  Metal  and  Casting. — Before  placing  the  metal  in 
the  melting  mold  or  crucible,  the  upper  portion  of  the  flask, 
including  the  crucible,  is  thoroughly  heated  with  a  large 
blue  flame  of  the  blowpipe.  This  precaution  is  to  assure  that 
the  upper  end  of  the  casting  mold  is  sufficiently  heated, 
thus  avoiding  the  granulated  effect  sometimes  seen  in  this 
portion  of  the  casting.  The  metal  is  placed  in  the  melting 
mold  and  a  yellowish  tinged  flame  of  the  blowpipe  played 
upon  it  until  it  is  thoroughly  melted,  as  indicated  by  the 
nugget  of  metal  settling  upon  the  floor  of  the  crucible, 
although  the  upper  surface  is  spheroidal.  The  metal  has 
the  property  of  holding  heat,  so  there  is  no  need  for  undue 
haste,  but  no  time  should  be  wasted  in  getting  the  metal 
cast.  The  gas  is  turned  off  the  gas  stove,  the  bail  is  attached 
to  the  bucket,  and  as  it  is  lifted  from  the  stove  the  chain  is 
made  straight.  The  swinging  of  the  bucket  is  started  with  a 
steady  long  swing,  avoiding  a  jerk  at  the  start  of  the  swing. 
The  diameter  of  the  swing  is  quickly  reduced  to  the  limit 
and  the  speed  increased.  The  motion  should  be  continued 
until  the  metal  has  crystallized.  This  will  probably  require 
from  fifty  to  one  hundred  revolutions. 

Philosophy  of  the  Casting  Process. — By  the  swinging  motion 
centrifugal  force  drives  the  molten  metal  down  the  feed  gate 
into  the  mold.  By  the  law  of  physics  (that  liquids  seek  their 
level)  the  molten  metal  will  rise  in  the  mold  and  vent  holes 
until  it  is  on  a  level  with  the  head  of  metal,  when  the  centrif- 
ugal force  will  condense  the  metal  until  the  hardness  of  the 
crystals  of  metal  and  centrifugence  are  equal.  This  will 
probably  be  when  the  metal  has  cooled  50°  to  100°  below  its 
fusing  point.  It  is  reasonable  to  suppose  that  the  metal  that 
has  travelled  the  farthest  from  the  head  of  metal  Mall  be  the 
first  to  set,  therefore  the  vent  sprues  and  the  palatal  border 
would  chill,  and  any  contraction  that  is  taking  place  will  be 
made  good  by  the  molten  metal  under  pressure  backing  it 


COOLING  AND  REMOVING  THE  CASTING        351 

up,  thereby  keeping  the  mold  full  and  providing  a  perfect 
fitting  base-plate.  The  ^mter,  by  careful  visual  observation, 
has  not  been  able  to  detect  the  defects  in  the  castings  made 
by  this  method  that  have  been  noticed  in  the  castings  made 
by  other  methods.  Therefore  the  writer  confidently  presents 
the  foregoing  method  as  the  best  yet  devised  for  casting 
aluminum. 

Suggestions. — Sufficient  free  space  must  be  provided  for 
swinging  the  bucket,  to  preclude  the  bucket  striking,  and 
dumping  the  molten  metal,  thus  endangering  the  person  of 
the  operator  and  nearby  property.  Such  accidents  are 
inexcusable.  It  is  well  for  an  inexperienced  person  to  prac- 
tice with  a  small  bucket  filled  with  water  and  describing 
the  same  radius  as  with  the  casting  outfit.  Confidence  will 
soon  be  gained  in  the  ability  to  start  and  stop  the  swing 
of  the  bucket.  If  a  bucketful  of  water  can  be  successfully 
handled,  a  crucible  mold  with  nearly  straight  sides  and  only 
half  full  of  molten  metal  should  be  harmless. 


Cooling    and    Removing  the  Casting.     After  swinging,  tlic 
ca.Hting  bucket  slioiiM  be  permitted  to  stiiiid  in  ;i  cool  place 


352 


ALUMINUM  BASE-PLATE 


for  fifteen  minutes,  after  which  the  coohng  may  be  expedited 
by  submerging  in  cold  water.     A  plaster  spatula  is  passed 


Fig.  240 


Fig.  241 


between  the  flask  and  the  investment,  when  by  pressure  upon 
the  loose  bottom  of  the  bucket  the  casting  and  investment 


FL ASKING 


553 


will  be  pushed  out  of  the  bucket.  The  hi  vestment  is  broken 
and  brushed  away  from  the  casting.  P^igs.  239  and  240  show 
a  casting  as  it  came  from  the  in\estment.  The  sprues  are 
snipped  away  and  the  edges  filed.  The  case  is  sandpapered 
and  buffed  with  felt  and  pumice  the  same  as  vulcanite. 

Caution. — Cast  aluminum  is  not  elastic,  therefore  care 
must  be  exercised  in  manipulating  light,  castings  not  to  bend 
them.  Probably  more  castings  are  warped  by  bending  than 
by  improper  casting.  Fig.  241  shows  a  trimmed  and  buffed 
aluminum  base-plate. 

Use  of  the  Aluminum  Base-plate. — The  base-plate  of  alumi- 
num is  to  be  used  the  same  as  the  Aulcanite  base-plate  for 
obtaining  the  occlusion  and  contour  wax  models,  mounting 
on  the  antagonizor,  setting  up  the  teeth,  proving  the  antag- 
onization  and  contour,  flasking,  packing,  vulcanizing,  and 
finishing. 

All  of  these  procedures  as  described  for  vulcanite  work 
are  sufficient  for  the  w  ork  in  hand,  excepting  for  flasking  and 
polishing. 

Fig.  242 


Flasking.     The  aluminum    base-plate  should    be   so   em- 
bedded in  the  first  half  of  the  xulcanite  flask  that  as  little 
(jf  the  metal  will  be  exi)osed  as  possible;  thus  a\'oiding  the 
.scraping  of  vulcanite  from  the  bulled   surface.     Fig.  242 
23 


354 


ALUMINUM  BASE-PLATE 


shows  a  case  suitably  encased  in  the  lower  section  of  the 
vulcanite  flask. 

Polishing. — Aluminum  may  be  scraped  the  same  as 
vulcanite,  but  it  may  be  dressed  down  easier  with  the 
emory  cloth  bands  on  the  lathe  arbor  (Fig.  131).  The  lathe 
should  be  run  at  high  speed,  and  light  pressure  used  in  holding 
the  work  against  the  abradent.  Scratches  are  removed  from 
the  surface  by  the  use  of  felt  buffers  and  pumice,  followed 
with  a  soft  brush  and  whiting.  This  gives  the  aluminum  a 
leaden  polish  due  to  fine  particles  of  the  metal  and  abradent 
being  ground  into  the  surface  of  the  metal  base-plate.  There 
are  three  methods  of  cleansing  and  developing  the  luster  of 
aluminum — (1)  chemical,  (2)  use  of  special  polishing  prepa- 
ration, and  (3)  burnishing.  The  chemical  method  consists 
of  treating  with  caustic  alkali  and  acids  alternately.  This 
method  is  hardly  suitable  for  the  dental  laboratory.  How- 
ever, it  gives  a  beautiful  frosted  eftect,  but  it  is  doubtful  if 
it  is  desirable. 

Fig.  243 


There  are  several  preparations  useful  for  the  second 
method.  Benzine  and  whiting  rubbed  on  with  a  buffer  of 
cotton  or  chamois  skin,  or  these  materials  used  by  hand. 
A  paste  may  be  made  of  two  drams  each  of  copper  sulphate 
and  potassium  carbonate  and  one  ounce  of  lard.     To  this 


POLISHING 


355 


paste  add  a  dram  or  two  of  any  one  of  several  finely  ground 
abradents,  as  chalk,  rotten  stone,  rouge,  tripoli,  or  buckhorn. 


Fig.  244 


Fig.  246 

'"itfm 

S^^A     y  '"■ 

jJF 

H|%     V,'^ 

jkSI 

JBI 

I           "'^ 

^^^L 

^ 

W0^ 

356 


ALUMINUM  BASE-PLATE 


The  burnishing  is  done  with  an  agate  or  bloodstone 
burnisher  and  a  burnishing  fluid  composed  of  equal  parts  of 
olive  oil  and  rum.  This  method  is  the  very  b6st  for  the 
maxillary  and  mandibular  surfaces,  but  is  open  to  the 
objection  that  it  shows  up  the  unequal  hardness  of  the  dressed 
surfaces.  However,  it  produces  the  hardest  and  best  wearing 
surface  of  any  of  the  methods  for  finishing.  Figs.  243, 
244,  and  245  show  different  views  of  completed  dentures  on 
aluminum  base-plates.  Fig.  246  shows  the  lingual  surface 
of  a  denture  with  the  metal  cast  to  the  teeth.  Figs.  247 
and  248  show  the  same  case  as  the  casting  came  from  the 
flask. 


_ 

) 

{ 

k^ 

JPfc*-5                     ^^& 

1 

mM 

% 

}< 

\ 

m' 

Casting  to  Porcelain  Teeth. — The  wax  model  must  be  so 
shaped  that  the  cast  metal  will  not  overlap  any  edges  of 
porcelain.  The  lingual  surface  of  the  denture  must  be 
carved  to  shape  in  the  wax  and  smoothly  finished.  Chloro- 
form can  be  used  to  finish  the  wax  surface.  The  flasked  case 
should  be  made  very  hot  before  pouring  the  metal ;  and  then 


CASTING  TO  PORCELAIN  TEETH 


357 


Fig.  248 


Fig.  249 


358  ALUMINUM  BASE-PLATE 

the  case  must  stand  until  it  is  cold  before  removing  from  the 
investment.  Platinum  pin  teeth  should  not  be  used,  as  the 
molten  aluminum  is  a  solvent  for  platinum.  The  labial  and 
buccal  surfaces  are  finished  with  vulcanite.  This  method 
is  of  doubtful  expediency.  Fig.  249  shows  the  Elgin  vacuum 
casting  machine.  Fig.  250  shows  the  method  of  forming 
the  wax  model  and  attaching  the  wax  sprue.  The  process 
consists  of  drawing  the  molten  metal  into  the  mold  by 

Fig.  250 


exhausting  the  air  in  the  mold,  through  the  investment 
compound,  with  a  pump.  It  is  not  reasonable  to  expect  that 
a  light  and  viscous  substance  like  molten  aluminum  can  be 
cast  as  sharply  and  densely,  and  with  as  much  certainty,  b}' 
negative  force  (suction)  as  by  positive  force  (centrifugal). 
However,  many  operators  are  much  pleased  with  the  machine 
and  its  achievements. 


SWAGED  ALUMINUM  BASE-PLATE 

Aluminum  may  be  swaged  by  either  the  die  and  counter  or 
the  machine  method. 


SWAGED  ALUMINUM  BASE-PLATE 


359 


Die  and  Counter  Method. — The  student  is  referred  to  the 
chapter  on  gold  base-plates  for  methods  of  constructing  a 
die  and  counter;  it  is  therefore  only  necessary  in  this  chapter 
to  discuss  tersely  the  use  of  such  a  base-plate. 


Fig.  251 


Formerly  the  most  successful  base-plate  of  aluminum  was 
made  by  the  swaging  method;  but  with  the  advent  of  modern 
casting  methods  the  order  has  been  changed,  and  the  writer 


360  ALUMINUM  BASE-PLATE 

cannot  conceive  of  any  case  in  which  the  swaged  base  of 
aluminum  would  be  preferable.  However,  it  is  well  to  have 
a  comprehensive  idea  of  the  manner  of  using  such  a  base- 
plate. 

A  suitable  die  and  counter  having  been  formed,  the  die  is 
oiled  (sperm  or  lard  oil)  and  a  sheet  of  well  annealed  No. 
18  or  20  B.  &  S.  gauged  aluminum,  with  its  fiber  at  right 
angles  to  the  raphe  of  the  mouth,  is  conformed  to  the  die 
w^ith  a  horn  mallet,  or,  better,  one  tipped  with  soft  vulcanite 

Fig.  252 


(a  cane  or  crutch  tip),  and  then  swaged  in  the  counter-die, 
using  a  heavy  swaging  hammer.  The  direction  of  the  grain 
is  important,  as  the  base-plate  is  easily  cracked,  in  use,  if  the 
fiber  is  parallel  with  the  raphe.  The  base-plate  having  been 
adjusted  to  the  mouth,  the  surface  is  prepared  to  hold  fast 
the  vulcanite  used  to  attach  the  teeth  by  scoring  the  surface 
with  an  engraver,  or  by  punching  loops  upon  the  surface. 
The  scoring  is  done  either  with  a  hand  engraver  or  an 
automatic  mallet  engraver.  The  loops  are  formed  with  a 
punch.  These  three  instruments  are  shown  in  order  in  Fig. 
251,  and  the  work  done  by  them  is  shown  in  Fig.  252.  The 
base-plate  is  scrubbed  with  soap  and  water  to  remove  oil 
and  dirt,  when  it  is  ready  to  be  used  in  forming  the  wax 
occlusion  and  contour  models.    It  is  flasked  for  vulcanizing 


SWAGED  ALUMINUM  BASE-PLATE 


361 


the  same  as  the  cast  ahiminum  base-plate.    It  is  also  polished 
in  the  same  manner. 

Machine  Swaging. — Various  machines  have  been  devised 
for  swaging  metal  base-plates;  they  are  better  adapted  to  the 
soft   metals  than  to  hard  ones.     The  principal  argument 


for  tlieir  existence  is  their  supposed  simplification  'of  con- 
structing dies  and  counters;  they  certainly  are  not  as  effective 
as  the  die  and  conntcr  method.  However,  there  is  a  use  to 
which  they  may  be  {lut  in  which  the  die  and  counter  cannot 


362 


ALUMINUM  BASE-PLATE 


readily  be  used;  that  is,  in  reswaging  a  base-plate  after 
attachments  have  been  made  to  it.  There  are  three  types 
of  these  machines: 


Fig.  255 


SWAGED  ALUMINUM  BASE-PLATE  363 

Type  No.  1  is  shown  in  Fig.  253;  it  is  known  as  the 
Parker  shot  swager  and  uses  dust  or  No.  12  shot  in  place 
of  a  counter-die.  A  heavy  swaging  hammer  furnishes  the 
power. 

Type  No.  2  is  illustrated  by  the  Olivian  swager  (Fig.  254), 
in  which  soft  rubber  gum  is  used  for  the  counter-die  and 
the  power  is  by  means  of  the  swaging  hammer  and  a  close- 
fitting  plunger. 

Type  No.  3  is  represented  by  the  Lyon  swager  (Fig.  255), 
and  differs  from  Type  No.  2  in  having  screw  pressure  act 
upon  the  plunger. 


CHAPTER    XI 

GOLD  AS  A  BASE-PLATE 

Material. — Pure  gold  is  a  bright,  rich,  yellow  metal,  with  a 
specific  gravity  of  19.26,  and  a  fusing  point  of  2016°  F.  It 
is  the  most  malleable  and  ductile  of  the  metals,  and  ranks 
third  as  a  conductor  of  heat  and  electricity.  It  is  insoluble 
in  any  of  the  ordinary  mineral  acids,  but  soluble  in  the 
combination  nitrohydrochloric  acid.  It  is  not  oxidized  by 
heat  alone,  therefore  is  a  noble  metal.  It  is  nearly  as  soft 
as  pure  lead,  and  can  be  alloyed  with  many  of  the  other 
metals.  It  is  used  in  prosthetic  dentistry  principally  in  its 
alloyed  state.  The  metals  with  which  it  is  alloyed  for  use 
in  plate  work  are  silver,  platinum,  copper,  and  zinc.  Silver 
has  little  effect  upon  it,  except  to  cheapen  it  and  modify  the 
color.  Platinum  alone  with  gold  has  little  effect  upon  it, 
but  in  combination  with  silver  and  copper  it  makes  the  gold 
very  hard  and  elastic.  Copper  alone  hardens  gold  very  much 
and  gives  a  deep  red-yellow  color.  Zinc  makes  it  hard  and 
brittle  and  increases  the  fusibility  markedly. 

There  are  two  classes  of  gold  used  in  plate-work  known 
technically  as  j^^f^f^  and  solder.  The  plate  is  that  form  of 
metal  containing  the  properties  of  hardness  or  softness; 
rigidity,  flexibility,  and  elasticity;  high  fusing  or  low  fusing, 
according  to  requirements  of  the  service  to  which  it  may  be 
put.  The  two  requirements  of  the  other  class  (solder)  are 
that  it  shall  appear  as  near  like  the  plate  upon  which  it  is 
to  be  used  as  possible,  and  melt  and  flow  at  a  considerably 
lower  temperature  than  the  plate. 

The  precious  metals  are  spoken  of  as  so  many  carats  fine, 
or  so  many  parts  of  24  pure;  thus  18  k  (carat)  gold  plate 
means  that  IS  parts  of  the  24  parts  of  the  alloy  are  pure 
gold  and  the  remaining  6  parts  consist  of  other  metals.  The 
required  carats  of  gold  for  base-plates  are  18  k  and  20  k, 
with  22  k  and  24  k  for  special  purposes.    A  suitable  formula 


TECHNIQUE  FOR  SWAGING  GOLD  365 

for  ISk  gold  plate  would  be  pure  gold,  18  parts;  pure  silver, 
4  parts,  and  pure  copper,  2  parts.  The  20  k  and  22  k  plate 
vvoidd  have  the  indicated  amount  of  pure  gold  with  the 
alloying  metals  of  equal  amounts  of  silver  and  copper.  The 
rigid  and  elastic  plate  known  as  clasp  gold  may  be  formed  of 
any  of  the  preceding  carat  by  substituting  platinum  for 
half  of  the  named  amount  of  silver.  Solders  are  formed  of 
the  same  degree  of  fineness  as  plate  by  substituting  zinc  for 
a  portion  or  all  of  the  silver.  This  was  formerly  true  of 
solders,  but  today,  as  the  result  of  competition  in  trade,  the 
solders  are  marked  "for"  the  indicated  carat  plate.  It  is 
known  that  the  solder  is  two  carats  lower  than  the  number 
upon  the  solder. 

Methods. — Base-plates  of  gold  are  formed  by  both  the 
swaging  and  casting  methods.  Swaged  gold  as  a  base  for 
artificial  dentures  has  been  the  standard  from  antiquity, 
and  especially  with  the  modern  revival  of  dentistry.  It  is 
especially  adapted  to  partial  cases  because  of  the  ease  with 
which  it  may  be  built  up;  its  rigidity,  strength,  and  com- 
pactness; and  its  purity  and  cleanliness.  For  most  full  cases 
it  is  inferior  to  continuous  gum.  The  casting  method  for 
gold  bases  has  but  one  feature  in  which  it  is  superior  to  the 
swaged  base  of  gold,  that  is,  adaptation.  In  all  other  factors 
(excepting  purity  of  material)  it  is  inferior  to  the  swaging 
method.  It  is  less  dense,  less  rigid,  less  elastic,  more  bulky 
for  the  required  strength,  and  consequently  more  expensive 
for  stock.  The  casting  method  for  gold  base-plates  should 
be  limited  to  small  saddles.  It  is  undesirable  for  full  dentures, 
bars,  bands,  ov  clasps.  (Jold  for  base-plates  needs  to  be 
rolled  or  drawn  in  order  to  flevelop  the  pr()i)erties  that  make 
it  most  desirable  for  the  base  of  an  artificial  denture. 


TECHNIQUE  FOR  SWAGING  GOLD 

Die  and  Counter  Method. — The  processes  involved  in  this 
method  are:  Taking  impression,  making  i)laster  cast  (or, 
better,  Spence  plaster  com])ound  cast),  model  for  die,  die 
and  counter,  and  swaging;  making  and  soldering  attachments. 


366 


GOLD  AS  A   BASE-PLATE 


Impression. — The  student  cannot  be  too  strongly  im- 
pressed with  the  fact  that  the  first  and  most  important 
element  for  success  in  any  kind  of  prosthetic  wx)rk  is  a 
suitable  impression,  and  that  the  impression  must  be 
taken  to  meet  the  requirements  of  the  individual  case. 
(See  Chapter  II.) 

Cast. — The  impression  may  be  filled  with  plaster,  or, 
because  of  its  strength  and  non-changing  properties,  Spence 
plaster  compound.  In  filling  the  impression  special  atten- 
tion should  be  given  to  developing  the  truncated  cone  form 
as  directed  in  the  chapter  on  casts. 


Fig.   250 


Model. — The  model  is  the  cast  prepared  for  molding  in  the 
sand.  The  model,  with  the  exception  of  its  face,  that  is,  the 
surface  made  by  the  impression,  must  be  so  shaped  that  it 
will  readily  draw  from  the  sand  mold.  This  will  require 
that  the  entire  body  of  the  model  will  slant  outward  to 
its  base  representing  a  truncated  cone.  This  may  be  accom- 
plished by  cutting  away  unnecessary  plaster  and  building 
out  deficiencies  with  wax.  The  thickness  of  the  model  will 
depend  upon  the  kind  of  molding  flask  used.  If  it  is  a  ring 
flask  (Fig.  256),  the  base  of  the  model  should  be  one  inch 
thick  at  the  thinnest  part  to  afford  the  required  strength 
to  resist  crushing.  If  the  molding  is  to  be  done  in  a  Bailey 
flask  (Fig.  257)  or  a  Lewis  flask  (Fig.  258),  or  the  die  is  to 


TECHNIQUE  FOR  SWAGING  GOLD 


367 


be  used  in  a  swaging  machine,  the  base  of  the  model  need  be 
but  a  quarter  or  a  half-inch  thick.    The  base  of  a  model  so 


Fig.  257 


Fig.  25S 


368 


GOLD  AS  A  BASE-PLATE 


shaped  could  furnish  no  obstacle  to  its  withdrawal  from  the 
sand  mold  (Fig.  259).  The  face  of  the  model  must  next  be 
studied,  to  know  that  it  will  draw  from  the  mold,  or  that 
its  conformation  is  such  it  will  be  keyed  in.  It  is  evident 
that  the  face  of  the  model  cannot  be  carved  to  obliterate 
undercuts,  but  that  means  must  be  devised  to  reproduce 
the  undercuts  in  the  die.  This  may  be  accomphshed  by  one 
of  three  ways — (1)  by  tilting  the  flask  in  drawing  the  model; 
(2)  by  the  use  of  cores;  and  (3)  by  a  specially  constructed 
parting  flask. 

Fig.  260 


The  first  method  answers  well  for  a  single  slight  undercut. 
This  is  illustrated  in  Fig.  260.  The  dotted  lines  represent 
lines  of  gravitation.  It  is  apparent  that  if  the  flask  is  held  at  a 
sufficient  angle  the  inlock  is  obliterated  and  the  model  may 
drop  without  defacing  the  mold.  The  slight  undercuts  that 
may  be  provided  for  by  this  method  are  located  at  the  incisal 
portion  of  the  alveolar  ridge  or  at  one  of  the  tuberosities. 

The  second  method  will  provide  for  any  and  all  cases  that 
may  present.  The  core  is  an  added  portion  used  to  fill  in  the 
undercut  and  contour  the  model  into  a  typical  truncated 
cone.  The  model,  having  been  varnished  with  shellac  and 
sandarac  (as  desirable  for  molding),  is  built  upon  with  a 
batter  of  investment  compound  (such  as  is  used  in  cast 
aluminum  work)  to  bring  the  model  to  the  desired  contour. 


TECHNIQUE  FOR  SWAGING  GOLD 


369 


For  strength  and  convenience  in  handling,  the  core  should 
be  about  one-half  an  inch  thick.  It  must  be  so  trimmed 
that  it  will  easily  drop  from  the  sand  mold  with  the  model; 


Fiu.  201 


FiG.  262 


the  c(jre  is  returned  to  its  seat  in  the  sand  mold  and  becomes 
a  part  of  the  mcjld.  When  the  investment  compound  has 
set  it  is- parted  from  the  model,  trimmed  as  smooth  as  pos- 
sible, and  then  placed  in  a  warm  place  to  dry.  it  should  be 
24 


370 


GOLD  AS  A  BASE-PLATE 


dried  to  such  an  extent  that  a  temperature  of  700°  or  800°  F. 
will  not  drive  steam  from  it.  This  can  be  done  in  an  hour's 
time  by  standing  it  on  its  edge  upon  a  sheet-iron  over  the 
gas  stove.  The  core  should  not  be  placed  on  its  side  while 
drying,  as  there  is  danger  of  warpage.  Fig.  261  shows  a  core 
for  the  anterior  undercut.  Fig.  262  shows  cores  covering 
the  entire  labial  and  buccal  surfaces  of  a  model.  The  core 
may  be  constructed  entire,  and  when  set  notched  nearly 


Fig.  263 


through  at  the  median  line,  and  broken  away  from  the  model. 
The  notch  should  be  wide  and  smoothly  trimmed.  Fig.  263 
illustrates  cores  for  the  lingual  surface  of  a  lower  model. 

Third  method:  Figs.  264,  265,  and  266  represent  Hawes' 
parting  flask.  This  flask  consists  of  two  rings,  the  bottom  of 
which  is  hinged  to  part  at  three  points. 

Molding. — There  are  a  variety  of  molding  sands  that  may 
be  used — the  iron  founder's  black  sand,  the  brass  founder's 


TECHNIQUE  FOR  SWAGING  GOLD 


371 


brown  sand,  and  marble  dust.  These  materials  require 
tempering  for  use.  If  the  material  is  used  daily  it  is  best 
tempered  with  water,  because  of  its  cleanliness;  but  if  it  is 
only  infrequently  used,  it  is  better  to  temper  it  with  glycerin 
or  sperm  oil,  as  with  these  materials  it  remains  ready  for  use 
for  a  considerable  time;  howe^Tr,  the  hot  metal  poured  upon 
them  produces  a  disagreeable  odor.  The  material  is  mixed 
with  the  chosen  liquid,  thoroughly  rubbed  and  sieved. 
They  improve  in  temper  by  standing  a  few  hours.  If  the 
molding  sand  is  in  a  suitable  condition  it  will  not  appear 
moist,  but  a  handful  thoroughly  compressed  in  the  hand 
will  break  with  a  clean  fracture. 


Fig.  264 


Technique. — The  morlel  (with  core  in  place  if  one  is 
rcf)nin'dj  is  rubbed  witii  talcum  j>()wder,  then  [placed  upon 
a  flat  surface  and  encompassed  with  the  ring  of  the  chosen 
molding  flask.  Molding  sand  is  sifted  into  the  flask  until 
it  is  one-third  full.  This  is  firmly  packed  with  the  fingers  aufl 
a  stick  ftami)ing  stick)  about  the  model,  more  sand  is  sifted 
in  and  i)ackcfl  firmly  down  npon  llic  face  of  the  model.  Sand 
is  added  until  the  ring  is  filled  flush.  The  flask  is  lifted  from 
the  bench,  turned   over  so  that  the  base  of  the  model  is 


372  GOLD  AS  A  BASE-PLATE 

upward,  a  thin  spatula  or  molding  trowel  is  passed  about 
the  edge  of  the  model  to  relieve  it  of  any  overlapping  sand. 
The  flask  is  again  turned  so  that  the  base  of  the  model  is 
downward;  if  there  is  a  slight  undercut  upon  the  model  not 
supplied  with  a  core,  the  flask  must  be  held  at  such  an  angle 
as  will  release  the  model  without  dragging  the  mold.  The 
sand  should  be  so  firmly  packed  about  the  model  that  it  will 
not  drop  of  its  own  weight.  The  model  is  released  from  the 
mold  by  gently  tapping  upon  the  side  of  the  flask  with  a 
light  weight  instrument,  as  a  wax  spatula.  If  the  mold  is 
not  perfectly  clean  and  smooth  at  the  first  attempt,  the 
operation  must  be  repeated  until  a  perfect  mold  is  obtained. 
Caution. — If  the  sand  is  overmoist  it  cannot  be  so  firmly 
packed  without  generating  steam  under  the  hot  metal  and 
thereby  spoiling  the  casting.  This  may  be  overcome  by 
packing  the  sand  less  firmly,  but  if  the  sand  is  not  compact 
enough  the  weight  of  the  metal  will  give  a  distorted  and 
useless  casting.  Therefore,  the  student  should  not  yield  to 
the  temptation  to  use  insufficiently  packed  sand.  He  should 
use  only  well  tempered  and  well  packed  sand. 

Accessory  implements  that  may  be  useful  are:  A  6-inch 
straight-edge  to  smooth  the  sand  flush  with  the  edge  of  the 
ring;  a  flat  ^-inch  ox-hair  paint  brush,  and  a  small  mouth 
blowpipe.     If  needed,  the  occasion  will  suggest  their  use. 

Metal  for  Die. — A  suitable  metal  for  a  die  should  possess 
hardness,  toughness,  sufficient  fluidity  to  take  a  sharp 
imprint,  and  should  be  moderately  low  fusing  and  non- 
shrinking.  There  are  three  types  of  metal  used  for  dies, 
namely:  (1)  A  shrinking  metal  (as  zinc);  (2)  non-shrinking 
(as  Haskell's  Babbitt  metal) ;  and  (3)  low  fusing  (as  the  low 
fusing  bismuth  compound) . 

Zinc. — ^Zinc  is  the  hardest  of  the  metals  commonly  used 
for  dental  dies,  but  it  shrinks  the  most  of  any  of  the  metals. 
The  advocates  of  this  metal  contend  that  the  shrinkage 
is  an  advantage,  that  it  assures  a  close  fit.  This  argument  is 
illogical,  for  if  an  impression  has  been  taken  to  meet  the 
requirements  of  the  case  all  subsequent  procedures  should 
require  exactness  and  not  counterbalancing  changes.      The 


TECHNIQUE  FOR  SWAGING  GOLD  373 

late  Professor  Buckingham  demonstrated  tliat  in  an  average- 
sized  zinc  die  the  shrinkage  is  about  4^  of  an  inch  across  and 
3^6^  of  an  inch  in  length.  Such  a  change  would  be  almost 
intolerable  upon  thin,  tense  tissue  or  properly  compressed 
soft  tissues.    However,  the  metal  is  much  used  for  dies. 

Babbitt  Metal. — There  are  many  alloys  on  the  market 
known  as  Babbitt  metal,  some  of  which  are  little  more  than 
lead,  and  all  of  the  hardware  store  stock  is  unreliable  for 
dental  purposes.  The  alloy  made  after  the  formula  of  Dr. 
L.  P.  Haskell  and  carried  by  the  dental  supply  houses,  meets 
the  requirement.  His  formula  consists  of  copper,  1  part; 
antimony,  2  parts;  and  tin,  8  parts  (c-a-t- 1-2-8). 

Care  should  be  used  not  to  overheat  this  alloy ;  in  fact,  no 
base  metal  or  alloy  should  be  heated  much  beyond  its  melting 
point.  There  are  two  reasons  for  this:  (1)  Oxides  are  formed 
and  occluded,  which  deteriorates  the  metal,  (2)  A  mixture 
of  metals  heated  much  beyond  the  fusing  point  tends,  upon 
cooling,  to  separate  into  definite  compounds,  mixtures, 
and  pure  metals,  and  to  congeal  according  to  the  fusing 
point  of  each;  thereby  forming  a  very  non-homogeneous 
mass.  The  student  should  be  interested  in  the  prevention 
rather  than  the  cure  for  this  undesirable  condition,  and 
exercise  care  in  heating  metals.  A  metal  or  an  alloy  of 
metals  should  be  heated  only  to  the  desired  fluidity,  so  as  to 
be  in  the  melted  state  as  short  a  time  as  possible.  As  it 
requires  considerable  time  for  a  mass  of  metal  to  liquefy, 
and  the  different  portions  will  have  absorbed  different 
amounts  of  heat,  and  the  liquefied  metal  is  rapidly  absorbing 
more  heat,  it  should  be  apjjarent  that  when  the  mass  is  half 
or  three-fourths  melted  that  it  has  absorbed  enough  heat 
for  liquefaction  and  should  be  removed  from  the  fire.  The 
pot  ha\'ing  been  removed  from  the  fire,  the  metal  is  stirred 
with  a  stick  of  wood  until  the  last  portion  of  metal  is  liquefied. 
SliouM  the  metal  be  too  viscid,  it  should  be  returned  to  the 
fire  and  stirred  for  a  moment,  when  it  will  be  ready  for 
jjouring. 

Jimnuth  Compound. — Bismuth  forms  some  wonderful 
alloys.     They  are  much  used  in  the  dental  laboratory.     Jt 


374  GOLD  AS,  A  BASE-PLATE 

constitutes  about  one-half  the  weight  of  the  very  low  fusing 
alloys.  It  and  antimony  are  the  only  metals  that  expand 
on  cooling.  Hodgen  states  that  bismuth  expands  3^  of  its 
volume.  Combined  with  lead,  tin,  and  cadmium,  it  forms 
alloys  all  of  which  melt  below  the  most  fusible  component, 
and  a  combination  may  be  made  to  fuse  as  low  as  140°  F., 
while  its  most  fusible  component  fuses  at  442°  F.,  and  its 
least  at  617°  F. 

Thus  the  three  principal  substances  for  dies  may  be 
summed  up  as:  Zinc,  fuses  at  773°  F.,  shrinks  the  most  of 
any  metal  on  cooling,  hardest,  and  brittle;  Babbitt  metal 
(Haskell),  fuses  at  500°  F.,  non-shrinking,  neither  as  hard 
nor  brittle  as  zinc ;  bismuth  alloy,  melts  below  boiling  water, 
non-shrinking,  and  is  less  hard  and  more  brittle  than  zinc. 

Counter-dies. — A  suitable  counter-die  must  be  prepared 
for  the  die.  It  is  desirable  that  the  counter-die  shall  be  of  a 
softer  and  more  fusible  material  than  the  die.  Softness  is 
required  that  the  compression  produced  in  swaging  shall  take 
place  in  the  counter  and  not  in  the  die ;  fusibility,  so  that  the 
counter  may  be  readily  formed  over  the  die.  Lead  fusing 
at  617°  F.  is  an  excellent  counter  for  zinc.  Four  or  five  parts 
of  lead  and  one  of  tin  fuses  at  about  the  same  temperature 
as  Babbitt  metal  (Haskell),  and  with  care  in  handling  forms 
a  desirable  counter-die.  A  counter-die  for  the  bismuth 
compound  alloy  may  be  formed  of  the  same  material  by 
first  "smoking"  the  die,  or  coating  with  whiting  wet  with 
alcohol,  and  careful  pouring.  Modelling  compound  serves 
well  as  a  counter,  or  the  die  may  be  driven  into  the  end  of  a 
block  of  soft  pine  and  it  used  as  a  counter.  In  the  swaging 
machines  various  substances  are  used  as  a  counter,  for  the 
bismuth  alloy  dies,  as  shot,  cornmeal,  sand,  tallow,  paraffin, 
or  rubber. 

Pouring  the  Die. — A  suitable  mold  having  been  obtained 
in  the  sand,  the  melted  metal  is  poured  in  until  the  mold  is 
full,  when,  if  the  Bailey  or  Lewis  flask  is  being  used,  the  top 
section  is  placed  and  the  pouring  continued  until  the  desired 
thickness  of  die  is  obtained. 

The  casting  or  die  should  stand  until  it  is  nearly  cold 


TEC  UNIQUE  FOR  SWAGING  GOLD  375 

before  removing  from  the  sand  mold,  as  the  metal  while  hot 
is  very  brittle  and  easily  broken  or  defaced. 

Making  the  Counter-die. — The  die  is  placed  upon  the 
molding  block,  and  sand  built  about  it  so  as  to  cover  all 
but  the  face;  that  is,  the  fac-simile  portion  of  the  mouth. 
The  sand  is  built  out  at  nearly  right  angles  to  the  die  for  two 
inches.  A  molding  ring  is  placed  about  the  embedded  die 
and  pressed  slightly  into  the  sand.  Sand  is  embanked 
about  the  encasing  ring  to  the  height  of  one-half  inch.  The 
counter-die  metal  is  phiced  in  a  clean  melting  ladle  or  pot, 
and  when  half  melted  removed  from  the  fire  and  stirred 
until  in  a  viscous  or  "mush-like"  state,  when  it  is  poured  or 
rather  dumped  upon  the  die.  There  should  be  about  twice 
the  quantity  of  counter-die  metal  melted  as  needed,  because, 
being  in  a  semifluid  state,  it  cannot  all  be  poured  nor  placed 
as  accurately  as  if  melted  into  a  more  fluid  state.  Plowever, 
the  excessive  quantity,  viscosity,  and  dumping  will  produce 
a  perfect  counter-die  without  danger  of  fusing  the  die.  If  the 
counter-die  metal  is  liquefied  and  poured  in  a  small  stream 
upon  the  die,  there  is  much  danger  that  a  portion  of  the 
surface  of  the  die  will  be  melted  and  the  die  and  counter 
spoiled;  and  a  portion  of  the  metal  so  contaminated  that  it 
should  not  be  used  again  for  either  a  die  or  a  counter.  There- 
fore, watchfulness  while  melting  the  metal  and  pouring 
while  the  metal  is  in  a  viscoid  state  will  save  time,  metal, 
and  vexation. 

The  die  and  counter-die  should  be  cleaned  of  sand  and 
examined  for  and  relieved  of  any  excrescences  on  their 
swaging  surfaces.  These  surfaces  are  oiled  as  a  i)reventive 
against  any  of  the  base  metal  adhering  to  the  metal  being 
swaged. 

Swaging  Gold  Plate. — A  suitable  pattern  for  cutting  the 
gold  plate  to  si'/e  should  be  made.  This  pattern  may  be 
made  of  any  thin  pliable  metal,  as  tinfoil  or  leadfoil.  Tea-lead 
or  tinfoil  of  about  20  gauge  serves  well.  The  supi)ly  honses 
carry  tinfoil  in  rolls  designed  for  this  use.  A  piece  of  pattern 
foil  is  placefl  ujjon  the  cast  and  nicel>'  conformed  to  its 
surface  by  pressure  of  the  fingers  and  thumbs;  it  is  removed 


376  GOLD  AS  A   BASE-PLATE 

and  trimmed  to  the  outline  of  the  desired  base-plate.  The 
pattern  base-plate  is  then  placed  upon  a  flat  surface  and 
pressed,  but  not  rubbed,  to  flatness. 

Gold  plate  of  a  suitable  composition,  carat,  and  gauge  is 
selected  for  the  work  in  hand,  the  pattern  is  placed  upon  it, 
and  its  outline  traced  with  a  sharp-pointed  instrument.  The 
plate  is  then  cut  to  the  outline  of  the  pattern  with  the  plate 
shears.  It  is  expedient  for  the  inexperienced  workman  to 
cut  the  gold  i  of  an  inch  larger  than  the  pattern  as  an  offset 
to  inaccurate  manipulation.  The  excess  gold  will  be  trimmed 
away  after  swaging  and  saved  as  scrap.  While  it  is  not 
essential,  it  is  advisable  to  cut  the  gold  so  that  the  fiber 
(crystals  elongated  by  rolling)  shall  be  across  the  denture. 

The  gold,  having  been  cut  to  pattern,  is  annealed  by  heating 
to  a  cherry-red  heat  and  cooling  in  water.  It  is  well  to 
re-anneal  the  metal  two  to  four  times  during  the  swaging 
process.  After  the  metal  has  been  upon  the  die  it  should  be 
wiped  to  remove  the  oil  and  any  adhering  base  metal  that 
may  be  upon  its  surface  before  heating. 

The  gold  is  conformed  to  the  die  with  a  horn  mallet  or 
one  tipped  with  rubber  (Fig.  267).  For  a  full  upper  base- 
plate the  conforming  is  begun  at  the  centre  and  extended 
in  concentric  rings  outward.  Care  must  be  exercised  at  all 
times  not  to  permit  the  gold  to  "buckle,"  that  is,  fold  upon 
itself.  Should  a  fold  begin  to  form,  it  must  be  straightened 
out  with  plyers,  annealed,  and  then  malleted  from  the  inner 
end  outward.  The  plate  should  be  well  conformed  to  the 
vault  before  any  attempt  is  made  to  carry  it  beyond  the 
crest  of  the  alveolar  ridge.  In  fact,  it  is  well  to  have  a  half 
counter-die  (one  made  to  cover  the  vault  portion  of  the 
die  only)  and  swage  the  vault  portion  before  endeavoring 
to  adapt  the  plate  to  the  labial  and  buccal  surfaces.  The 
swaging  is  done  with  a  heavy  swaging  hammer.  A  few  dead 
blows  should  be  used.  The  horn  mallet  is  used  with  a  light 
elastic  blow,  thereby  marring  the  gold  the  least,  whereas  the 
swaging  hammer  is  used  with  a  dead  pushing  blow,  thereby 
conforming  without  a  backward  spring,  and  with  less  harden- 
ing of  the  gold.    In  swaging  difficult  cases,  that  is,  high  vaults 


TECIIXIQVE  FOR  SWAGING  GOLD 


877 


and  heavy  undercut  ridges,  it  is  well  to  clamp  the  plate  and 
half-counter  to  the  die  with  a  C  clamp  (Fig.  268)  while 
carrying  the  labial  and  buccal  flange  to  place  with  the  horn 
mallet.  (This  illustration  shows  a  full  lower  base  plate.) 
For  this  part  of  the  conforming  a  horn  mallet  with  the  small 
end  filed  to  a  blunt  edge  is  preferable.  Should  the  die  be  of 
the  V-shape  type  the  conforming  may  be  more  easily  done 


Fig.   20, 


by  slitting  the  labial  flange  in  the  median  line  nearly  to  the 
crest  of  the  ridge.  The  edges  are  permitted  to  overlap,  and 
later  are  soldered.  The  base-plate  being  well  conformed 
with  the  horn  mallet,  it  is  wiped  of  oil  and  base  metal.  As  the 
plate  must  be  annealed  before  the  heavy  swaging,  it  should 
i)e  thoroughly  inspected  for  evidences  of  adhering  base  metal 
from  the  die.  Should  any  })e  detected  that  cannot  be 
wiped  away,  it  nuist  be  "pickled."    The  pickling  is  done  by 


378 


GOLD  AS  A  BASE-PLATE 


boiling  in  a  solution  of  nine  parts  of  water  and  one  of  sul- 
phuric acid,  in  a  copper  acid  pan.  (In  forming  the  pickle 
pour  the  acid,  a  little  at  a  time,  into  the  water.  An  explosion 
is  liable  to  occur  if  the  water  is  poured  into  the  acid.)  The 
base-plate  having  been  well  conformed  with  the  mallet,  it 
is  placed  in  the  oiled  counter-die  and  struck  a  heavy  dead 
blow.    It  is  then  removed  from  the  counter-die  and  inspected. 

Fig.  2GS 


If  a  buckle  is  forming,  it  should  be  corrected  with  the  plyers 
and  mallet,  then  returned  to  the  counter-die  and  struck  one 
dead  blow  and  again  removed  and  inspected.  When  the 
buckling  tendency  ceases  it  is  thoroughly  swaged. 

It  should  be  apparent  to  the  student  that  a  metal  base- 
plate conformed  and  swaged  over  one  die  cannot  accurately 
fit  the  mouth  for  the  reason  that  the  force  of  all  the  blows 


TECHNIQUE  FOR  SWAGING  GOLD 


379 


struck  upon  the  base-plate  must  be  received  upon  the  high 
points  (rugse  and  ridges)  of  the  die;  therefore,  the  elevated 
portions  of  the  die  are  compressed  or  "battered  down." 
This  condition  can  only  be  offset  by  annealing  and  swaging 
in  a  well-oiled  second  die  and  counter-die. 

When  molding,  two  dies  and  counters  should  be  formed, 
the  better  die  and  its  counter  to  be  reserved  for  the  final 
swaging.  If  a  very  stiff  base-plate  material  (as  clasp  metal) 
is  being  swaged,  three  or  more  dies  and  counters  will  be 
required. 


Fig,   209 


Swaging  Full  Lower  Base-plates.— 'i'he  gold  cut  to  pattern 
is  amiealed  and  grooved  with  tin-  plate  benders  (Fig.  L'C.O) 
then  conformed  to  the  oiled  die,  beginning  ujion  the  Inigua 
side  of  the  ridge.     When  the  base-plate  has  been  mallet cd 
for  some  time  it  may  seem  (jiiite  recalcitrant,  and  it  should 
then   be  cleaned,  annealed,  and   swaged  one  stroke  ni  the 


380 


GOLD  AS  A  BASE-PLATE 


counter,  which  will  much  aid  the  conforming  with  the  mallet. 
In  a  high  ridged  case  a  half  counter-die,  covering  the  lingual 
surface  only,  will  be  useful  (Fig.  268).  The  swaging  is 
accomplished  in  the  same  manner  as  for  the  upper. 

Swaging  Partial  Cases. — Fig.  270  shows  a  properly  shaped 
model.    The  teeth  stumps  should  be  about  -^  to  y^  of  ^^ 


Fig.  271 


Fig.  272 


inch  long,  just  enough  to  give  and  keep  a  clear  outline  of 
the  teeth,  about  which  the  base-plate  is  fitted  by  swaging, 
nipping  with  the  plate  nippers  (Fig.  271),  and  filing  with  a 
rat-tail  or  half-round  metal  file  (Fig.  272). 
The  counter-die  for  partial  cases  should  extend  but  little 


TECHNIQUE  FOR  SWAGING  GOLD 


381 


farther  than  the  face  of  the  die.  Many  operators  embed  the 
die  for  both  partial  and  full  cases  deeply  in  the  counter.  This 
practice  is  worse  than  useless,  because  it  is  a  trouble  maker. 
In  forming  the  counter-die,  all  portions  of  the  die  not 
desired  to  be  covered  with  the  counter  are  embedded  in  the 
molding  sand.  For  half-counters  the  sand  is  built  flush 
with  or  a  Httle  higher  than  the  crest  of  the  alveolar  ridge, 
when  a  small  molding  ring  is  set  in  place  and  the  counter- 
die  metal  poured  into  it. 

Doublers. — A  doubler  is  a  piece  of  metal  fitted  and  soldered 
to  the  lingual  surface  of  the  base-plate  to  give  additional 
strength  and  rigidity.  These  are  especially  required  for 
partial  cases.  The  doubler  is  usually  formed  of  the  same 
carat  and  gauge  gold  as  the  base-plate,  although  it  may  be 
formed  of  a  more  rigid  alloy  than  that  of  which  the  base-plate 
is  being  formed,  especially  if  a  very  high  carat  gold  is  used. 
The  doubler  should  be  placed  so  as  to  receive  the  greatest 
strain  that  is  placed  upon  the  base-plate;  and  to  interfere 
with  the  tongue  and  speech  as  little  as  possible.  The  doubler 
may  cover  but  a  small  portion  of  the  base-plate  or  it  may 
cover  nearly  the  whole  surface.  It  should  be  at  least  enough 
smaller  than  the  base-plate  to  form  a  ledge  upon  which  the 
solder  is  placed  while  soldering,  and  thereby  forming  a  less 
noticeable  joint. 


Forming  the  J)ovhler.—A  pattern  is  formed  by  pressing, 
with  the  fingers,  a  i)iece  of  i)attern  tin  over  the  base-plate, 
and  trimming  to  the  desired  form.  The  outline  of  the  pattern 
is  traced  upon  the  sheet  of  metal  to  be  \ised,  then  cut  with 


382  GOLD  AS  A  BASE-PLATE 

the  plate  shears.  The  doubler  is  conformed  by  the  mallet 
to  the  first  die  and  swaged.  It  is  then  cleansed,  annealed, 
placed  upon  the  base-plate  over  the  second  die,  and  swaged. 
The  edge  is  then  filed  to  a  bevel  with  the  bevel  on  the  outside 
of  the  doubler.  This  bevelling  is  to  aid  in  the  finishing, 
as  the  joint  between  the  doubler  and  base-plate  should  be 
as  nearly  imperceptible  as  possible.  The  base-plate  and 
doubler  having  been  cleansed  by  pickling,  the  under  surface 
of  the  doubler  is  smeared  with  a  fine  ground  or  liquid  flux, 
clamped  to  the  base-plate  with  wire  clamps  (Fig.  273) 
and  soldered. 


TECHNIQUE  OF  GOLD  SOLDERINQ 

The  necessary  equipment  for  soldering  gold  is  not  large, 
but  should  be  well  chosen  and  their  properties  and  use  well 
understood.  The  necessary  equipment  consists  of  a  good 
investment  compound,  holders  or  supports  for  the  work, 
flux,  and  a  blowpipe. 

Investment  Compound. — There  are  a  number  of  good  invest- 
ment compounds  on  the  market.  Or  one  made  after  the 
formula  given  on  page  341  will  meet  every  requirement. 
The  investment  should  withstand  the  heat  to  which  it 
will  be  subjected  without  fusing  or  cracking,  and  it  should 
conduct  heat  readily.  Unfortunately  the  bond  (plaster  of 
Paris)  that  is  used  in  the  investment  compounds  fuses  at 
a  low  temperature  (1100°  F.,  Price),  shrinks  badly,  and  is 
a  poor  conductor  of  heat.  Therefore,  only  enough  plaster 
of  Paris  should  be  used  to  give  binding  strength.  The  com- 
pound should  have  as  few  basic  ingredients  as  possible,  be- 
cause it  is  a  well-known  metallurgical  fact  that  two  or  more 
high  fusing  basic  substances  may  at  a  moderately  low  tem- 
perature form  low  fusing  compounds.  Another  factor  to  be 
taken  into  account  in  selecting  an  investment  is  that  a  mate- 
rial in  a  fine  state  of  subdivision  is  more  fusible  than  in  a 
coarse. 


TECHNIQUE  OF  GOLD  SOLDERING  383 

Holders. — Holders  are  of  two  types,  as  blocks  composed 
of  charcoal,  asbestos,  or  magnesia;  and  appliances  serving 
the  double  purpose  of  holder  and  heater. 

The  charcoal  block  is  chemically  treated  so  that  it  burns 
only  while  in  contact  with  a  flame,  therefore  is  safe  to  use 

Fig.  274 


in  the  laboratory.  This  is  not  true  of  a  block  of  ordinary 
charcoal.  The  charcoal  block  is  the  best  made  for  certain 
purposes,  as  it  adds  to  the  heat  of  the  blowpipe  flame  and 
aids  in  deoxidizing  metals.  Its  disadvantages  are  that  it  is 
black,  brittle  (both  overcome  l)y  encasing),  and  is  rai)idly 
consumed.  It  is  not  suitable  as  a  support  for  metals  to  be 
oxidized,  nor  working  j)latinum.  The  asbestos  blocks  are 
cleanly,  durable,  and  fire-proof,  but  otherwise  nothing  to 


384 


GOLD  AS  A  BASE-PLATE 


commend  them.  The  magnesia  blocks  are  compact,  cleanly 
to  handle,  qnite  durable,  and  so  soft  that  some  forms  of  work 
may  be  embedded  in  its  surface  and  thus  be  better  supported. 
Figs.  274  and  275  show  two  combined  supports  and  heating 
appliances. 


Fig.  275 


Flux. — Term  derived  from  fluo,  fiuxus,  to  flow,  and  is 
applied  in  metallurgy  to  those  substances  that  cleanse  and  aid 
the  flow  of  metals.  In  hard  soldering  (solder  that  requires 
a  red  or  higher  heat  to  melt)  the  alkali  salts  (preferably 
sodium  borate  [borax])  are  used — to  cleanse  the  surface  to 
be  soldered  by  absorbing  the  oxides  and  preventing  oxida- 
tion and  making  fluid  the  solder.  For  soft  soldering  (solder 
that  requires  less  than  red  heat)  zinc  chloride  and  organic 
substances,  as  stearic  acid,  rosin,  etc.,  are  used. 

Blowpipe. — The  blowpipe  is  an  instrument  of  simple  and 
complex  construction,  for  directing,  increasing  the  heat,  and 
concentrating  the  flame  in  metallurgical  work. 

The  mouth  blowpipe  is  of  the  simple  type,  and  consists  of 


TECHNIQUE  OF  GOLD  SOLDERING 


385 


a  tapered  tube  either  straight  or  bent,  and  is  operated  with 
the  mouth  by  forming  a  bellows  of  the  cheeks.  This  is  an 
excellent  instrument  for  light,  quick  service.  However,  it  is 
questionable  if  it  is  profitable  for  the  student  to  spend  his 
time  in  mastering  its  technicjue,  especially  for  large  cases, 
when  there  are  so  many  excellent  mechanical  devices  for 
doing  this  work. 

The  mechanical  blowpipe  is  more  or  less  complex.  There 
are  many  forms  of  this  instrument  designed  to  develop 
certain  features  for  its  use.  As  these  various  forms  are 
described  in  all  the  reference  books  on  prosthesis,  one  only 
will  here  be  shown  as  an  illustration. 


AIR  OUTLET 


The  "Automaton"  (Fig.  275)  is  designed  to  be  and  is  to 
an  extent  automatic.  Gas  is  admitted  to  the  pipe  by  the 
anterior  tube  and  air  l)y  the  posterior  tube.  The  pipe  is 
equippcfl  with  a  sliding  arrangement  of  its  barrel,  which 
automatically  regulates  the  quantity  of  gas  and  air,  provided 
the  supply  of  gas  and  air  are  under  suitable  pressure. 

The  air  })last  is  furnished  either  by  a  foot  bellows,  a 
compressed  air  tank,  or  power  air  pump.  A  very  ingenius 
and  efficient  air  pump  known  as  the  "Vernon  ilotary  Com- 
2o 


386  GOLD  AS  A  BASE-PLATE 

pressor"  has  recently  been  put  upon  the  market  by  the  Lee 
S.  Smith  &  Son  Company.  It  is  only  3  inches  high,  \\ 
inches  thick,  and  weighs  two  and  one-half  pounds.  It  is 
designed  to  be  coupled  to  the  electric  lathe  or  any  small 
power  in  the  office.  Fig.  276  shows  the  complete  machine 
and  Fig.  277  its  internal  construction. 

Fig.  277 


Use  of  the  Blowpipe. — On  page  231  the  Bunsen  burner  is 
described  as  a  tube  with  an  opening  near  the  bottom  for 
the  admission  of  air  to  the  gas  by  natural  draft.  In  the 
blowpipe  the  air  is  forced  into  the  flame,  which  gives  a 
greater  range  of  possibilities.  The  object  of  the  flame  is 
to  produce  heat.  Heat  is  a  result  of  chemical  action  mani- 
fested in  the  oxidation  of  the  carbon  and  hydrogen  of  the 
fuel.  It  is  obvious  that  oxidation  can  be  controlled,  hence 
the  degree  of  heat  and  its  usefulness.  Therefore  the  object 
of  the  blowpipe  is  to  create,  direct,  and  control  heat.  The 
blast  of  air  increases  the  amount  of  oxygen,  the  rapidity  of 
oxidation,  and  heat  up  to  a  certain  point,  after  which  an 
increasing  blast  cools  the  combining  gases  until  the  temper- 
ature is  reduced  below  the  ignition  point  and  the  flame 
is  extinguished,  "blown  out."  It  is  impossible  for  the 
operator  to  tell  when  he  has  reached  exactly  the  highest 
degree  of  heat  and  the  flame  is  beginning  to  cool.  However, 
he  knows  that  a  j^ellow  tinge  indicates  carbon  imperfectly 


TECHNIQUE  OF  GOLD  SOLDERING  387 

combined  with  oxygen,  and  that  the  bhie  color  in  the  outer 
two-thirds  of  the  length  of  the  flame  indicates  perfect  com- 
bustion and  that  the  point  of  highest  temperature  is  being 
approached  or  passed.  (The  flame  is  always  blue  at  its 
base,  but  this  is  because  the  carbon  has  not  yet  reached  the 
yellow  stage.)  Therefore,  a  yellow  flame  indicates  a  com- 
jiaratively  low  degree  of  heat,  and  that  as  the  blast  is  in- 
creased the  temperature  increases  with  the  disappearing 
yellow  color;  that  the  succeeding  blue  color  indicates  perfect 
combustion,  and  that  the  temperature  is  increasing  until 
the  highest  degree  is  attained,  and  then  an  increasing  blast 
chills  the  flame  until  it  is  below  the  ignition  point  and 
extinct. 

Fig.  278 


The  blowpipe  flame,  like  the  Bunsen  flame,  has  three 
zones;  the  inner  or  gaseous  zone,  the  middle  or  combustion 
zone,  known  as  the  reducing  flame,  and  the  outer  mantle  or 
oxidizing  flame.  The  diagram  shown  in  Fig.  27S  illustrates 
the  three  zones,  .1,  B,  C.  Work  to  be  heated  and  soldered 
should  be  placed  in  the  reducing  flame  at  B'B',  where  it 
will  be  heated,  cleaned  of  any  oxides,  and  the  solder  nicely 
flowed ;  but  if  the  work  is  j)laced  at  C'C  or  advanced  to  C 
the  work  will  be  made  dirty  by  oxidation  and  be  endangered 
of  burning.  The  soldering  can  be  done  at  this  portion  of 
the  flame  only  by  the  use  of  an  excessive  amount  of  flux. 

The  flame  is  used  either  in  the  form  of  a  brush  or  a  needle. 
These  are  easily  produced  with  a  mouth  blowpipe  by  having 
rlie  nfjzzle  outsirle  of  the  flame  for  the  brush  form  and  in  for 
the  needle.  The  same  results  are  obtained  with  the  automaton 
by  using  a  large  flow  of  gas  and  light  air  pressure  for  the 
brush  and  a  small  flow  of  gas  and  a  moderately  heavy  air 
pressure  for  tlie  needle  flame. 


388  GOLD  AS  A  BASE-PLATE 


SOLDERING  ATTACHMENTS  TO  THE  GOLD  BASE- 
PLATE 

There  are  three  classes  of  attachments,  known  as  strength- 
eners,  finishers,  and  retainers. 

The  strengthener  may  be  in  the  form  of  a  doubler  or 
wire.  The  wire  strengthener  may  serve  as  a  finisher,  while 
the  finisher  is  always  a  strengthener. 

Soldering  Doublers. — The  base-plate  and  doubler  having 
been  pickled  and  thoroughly  cleaned,  the  doubler  is  smeared 
on  the  under  surface  with  a  fine  ground  cream  or  paste  of 
borax.  (If  desired  the  proprietary  fluxes  in  the  supply  houses 
may  be  used.  They  are  composed  principally  of  borax.) 
The  base-plate  and  doubler  are  firmly  pressed  together  and 
clamped  with  wire  clamps.  (See  Fig.  273.  These  clamps 
are  formed  of  soft  iron  wire,  gauge  15.)  Solder,  two  carats 
lower  than  the  base-plate,  is  cut  in  pieces  i  by  |  or  |^  by  j 
of  an  inch,  fluxed,  and  placed  upon  the  base-plate  at  the  edge 
of  the  doubler  for  one-half  of  its  circumference.  The  work 
is  supported  upon  a  soldering  block,  preferably  of  charcoal, 
with  the  solder  decked  edge  elevated.  The  yellow- tinged 
brush  flame  is  applied  to  the  base-plate  and  doubler  with 
the  greater  heat  at  the  farther  side  of  the  doubler  from  the 
solder.  This  will  cause  the  solder  to  flow  between  the  base- 
plate and  doubler  and  completely  fill  the  space  between 
them.  The  solder  flows  between  the  two  plates  of  metal  in 
place  of  running  away,  because  of  three  physical  laws,  as 
follows:  (1)  Solder  always  flows  to  the  hottest  point.  (2) 
Capillary  attraction.  (3)  Gravitation.  Should  every  por- 
tion of  the  joint  not  be  filled  at  the  first  flush,  more  solder 
should  be  added,  at  the  deficient  point,  and  flowed.  No 
attempt  should  be  made  to  remelt  the  first  flush  of  solder. 
The  case  is  pickled  to  remove  the  flux  and  reswaged  in  the 
last  die  and  counter  by  two  or  three  dead  blows  of  the 
swaging  hammer. 

Soldering  Finishers. — A  gold  base-plate  that  is  to  have  the 
teeth  attached  with  vulcanite  should  have  a  finisher  provided 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE    389 

for  the  joining.  However,  the  finisher  is  often  omitted  as  a 
means  of  sa\ing  labor  and  expense,  but  always  at  the  expense 
of  strength  and  perfection.  The  finisher  may  be,  in  form, 
either  thin  plate  or  wire.  Upon  the  buccal  and  labial  surfaces 
the  thin  plate  finisher  may  be  formed  either  by  turning  the 
edge  or  soldering  on  a  swaged  piece  of  plate.  Finishing  the 
lingual  surface  of  the  joining  with  thin  plate  can  only  be 
accomplished  by  swaging  and  soldering  an  extra  piece  of 
metal.  A  wire  soldered  about  the  periphery  of  the  joining 
is  the  neatest,  strongest,  and  best  way  of  forming  a  finisher. 

Turning  the  Edge  of  Base-plate. — If  a  turned  edge  of  the 
labial  and  buccal  surfaces  of  the  base-plate  is  desired,  the 
impression  is  prepared  by  marking  the  required  outline  of 
the  edge  of  the  base-plate  and  carving  away,  at  right  angle 
to  the  median  plane  of  the  impression,  the  border  of  the 
impression  to  the  indicated  outline.  This  will  result  in  the 
forming  of  a  ledge  upon  the  die  that  will  turn  the  edge  of  the 
plate  at  right  angle.  The  balance  of  the  turning  is  done  with 
pliers. 

Swaging  and  Soldering  the  Labial  and  Buccal  Finishers. — For 
this  purpose  wax  occlusion  and  contour  models  are  obtained, 
the  case  placed  on  the  antagonizor,  teeth  mounted,  gum 
portion  restored  either  with  porcelain  sections  or  wax;  when 
an  impression  is  obtained  of  the  surface  for  which  the 
finisher  is  to  be  formed,  the  model,  die,  and  counter  formed; 
and  the  finisher  swaged.  The  finisher  will  be  in  two  sections, 
each  extending  from  the  median  line.  The  teeth  and  wax 
are  removed  from  the  base-plate  in  a  mass  by  warming  the 
under  surface  of  the  base-plate.  The  finisher,  l)oraxed,  is 
(•lami)ed  to  the  base-plate  with  wire  clamps,  solder  jjlaccd 
in  the  crevice  and  drawn  outward  by  the  blowpipe  flame. 

The  .same  i)rocedure  is  required  for  forming  the  lingual 
thin  plate  finisher.  However,  the  work  is  carried  on  at  the 
same  time  (not  after)  as  the  buccal  and  labial  finisher. 

This  method  necessitates  much  labor  and  mechanical 
skill,  and  when  completed  is  neither  as  strong  nor  cleanly 
as  the  wire  finisher. 


390 


GOLD  AS  A  BASE-PLATE 


Wire  Finisher. — This  finisher  is  formed  by  using  an  18  or 
possibly  a  16  B.  &  S.  gauged,  20  k,  gold  wire,  and  forming  it 
to  the  base-plate.  The  conforming  is  done  by  bending  the 
annealed  wire  with  the  fingers  and  pliers  so  as  to  approxi- 
mate the  periphery  of  the  base-plate.  Begin  at  either 
tuberosity  and  conform  the  wire  for  one  inch,  attach  with 
wire  clamps  placed  at  both  ends  of  the  conformed  portion, 
place  a  small  portion  (size  of  the  head  of  a  pin)  of  boraxed 
solder  at  some  point  of  contact,  and  melt.  Continue  the 
conforming  and  tacking  an  inch  at  a  time  until  the  wire  is 

Fig.  279 


Fig.  280 


carried  the  entire  length  of  the  joining  of  the  base-plate,  and 
vulcanite.  The  base-plate  is  placed  upon  the  die  and  the 
tacked  wire  closely  adjusted  to  the  base-plate  for  its  entire 
length.  This  may  be  done  with  a  plate  burnisher  (Fig.  279 
is  the  Prothero,  and  Fig.  280  is  the  Wilson  plate  burnisher),  or 
a  small  copper  riveting  hammer  may  be  used.  The  base- 
plate is  removed  from  the  die  and  inspected  for  base  metal. 
The  crevice  is  smeared  with  flux  and  a  generous  quantity  of 
solder  placed  along  the  upper  edge  (as  supported  on  the  block) 
of  the  wire  for  its  entire  length ;  it  is  supported  on  a  soldering 
block  and  the  yellow  tinted  blowpipe  flame  applied  care- 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE    391 

fully  over  the  whole  surface  of  the  base-plate  until  the  flux 
is  dry,  when  the  flame  is  placed  at  either  tuberosity  and 
concentrates  at  the  lower  edge  of  the  wire,  thereby  fusing 
and  drawing  into  place  the  solder,  advancing  piece  by  piece 
until  all  is  fused. 

Fig.  281 


Fig.  282 


Fig.  283 


Retainers. — Retainers  are  loops  soldered  to  the  base-plate, 
about  which  the  vulcanite  is  attached.  It  is  obvious  that  the 
greatest  efficiency  of  the  retainers  is  at  the  i)crij)liery  of  the 
joining.    They  are  formed  of  wire,  or  narrow  strips  of  scrap 


392  GOLD  AS  A  BASE-PLATE 

gold  plate,  convoluted.  The  convoluted  strip  or  wire  is 
clamped  to  the  base-plate  and  soldered.  Figs.  281  and  282 
show  a  gold  base-plate,  with  the  vulcanite  removed,  that  was 
worn  for  some  years.  Figs.  283  and  284  show  a  completed 
denture. 

Fig.  284 


Warping  in  Soldering. — The  base-plate  is  subject  to  warping 
by  unequal  expansion  of  the  metal  while  soldering.  This 
can  hardly  be  avoided.  Base-plates  are  often  unnecessarily 
warped  by  clamping  to  the  soldering  block  with  a  spring 
clamp.  When  all  metal  attachments  have  been  made  to  the 
base-plate  it  is  placed  upon  the  die  and  inspected;  if  any 
rocking  or  springing  appears  as  pressure  is  applied  on 
different  portions  of  the  base-plate,  it  should  be  placed  in 
a  swaging  machine,  as  the  Parker  shot  swager,  and  reswaged. 

The  base-plate  is  now  tried  in  the  mouth,  and  if  satisfactory, 
wax  is  built  upon  it  for  the  occlusion  and  contour  models; 
when  the  subsequent  procedures  are  the  same  as  for  a  vul- 
canite denture. 

Soldered  Gold  Artificial  Dentures. — Prior  to  the  introduc- 
tion of  vulcanite  the  teeth  were  soldered  to  the  base-plate. 
This  necessarily  was  a  very  unsanitary  appliance.  There 
is  no  logical  or  practical  reason  why  such  a  denture  should 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE    393 

be  inserted  at  this  stage  of  the  development  of  dental  pros- 
thetics. However,  there  are  a  few  cases  in  which  a  modified 
form  of  the  method  may  be  of  the  greatest  service.  Fig. 
285  shows  the  lingual  surface  of  such  a  partial  denture.    The 

Fig.  285 


patient  for  whom  this  appliance  was  constructed  had  a  very 
long  upper  lip  and  the  lower  teeth  shut  very  close  to  the 
upper  gum.  Facings  were  backed  with  26  gauged  clasp 
gold,  backings  closely  fitted  to  the  base-plate,  invested,  and 
soldered.       The    labial    gum   restoration  was    made    with 


vulcanite.     Fig.  280  shows  tiie  labial  aspect  of  the  same 
case. 

There  are  some  partial  ca.ses  which  rcfpiirc  no  gum  resto- 
ration, that  because  of  the  close  shut  will  require  a  metal- 
backed  facing  soldered  to  the  gold  base-plate;  or  if  the  base- 


394 


GOLD  AS  A  BASE-PLATE 


plate  is  to  be  vulcanite  a  metal  tang  of  clasp  metal  is  soldered 
to  the  backing  of  the  facing  and  extended  backward  into  the 
vulcanite  base-plate.  Fig.  287  shows  such  a  facing  backed 
and  tanged.  Bicuspids  for  very  close  shut  cases  may  be 
provided  with  a  porcelain-faced  gold  dummy  (such  as  is  used 
in  bridge-work)  soldered  to  the  base-plate.  For  molars  the 
facing  may  be  better  omitted. 


Soldering  Porcelain  to  Metal  Base-plate. — This  work  requires 
that  a  stiff  rigid  plate  of  metal  be  closely  fitted  and  attached 
to  the  facing  with  solder;  or  the  facing  may  be  backed  with 
either  35  gauged  pure  gold  or  platinum,  invested  and  con- 
toured with  22  k  solder.  The  facings,  however  backed,  are 
adjusted  to  the  base-plate  and  soldered. 


Fig.  288 


Fitting  the  Backings. — Tinfoil  patterns  are  made  of  the 
backings  and  traced  upon  the  gold  to  be  used.  It  is  well, 
as  a  precaution  against  inaccurate  workmanship,  to  punch 
the  pinholes  before  cutting  the  backing  from  the  stock 
piece.  The  English  double  punch  (Fig.  288)  may  be  used, 
and  punch  both  holes  at  the  same  time,  or  the  single  punch 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE     395 

(Fig.  289)  may  be  used  and  punch  the  holes  separately. 
If  the  double  punch  is  used  the  tooth  to  be  backed  will 
adjust  the  piuich,  while  with  the  single  punch  the  plate 
must  be  marked  for  the  punch.  This  may  be  done  by  slightly 
smearing  the  metal  with  wax  and  pressing  the  pins  of  the 
tooth  into  it,  or  tinfoil  punctured  by  the  pins  of  the  tooth 
may  be  laid  upon  the  metal  as  a  guide  to  punching.    The 

Fig.  289 


backing  is  conformed  to  the  facing  as  closely  as  possible 
by  bending.  'J'he  edges  are  filed  to  a  })evel  and  burnished 
to  tlic  facing.  The  facing  and  its  })acking  are  temporarily 
held  together  l)y  ttirning  down  ;i  shaving  from  the  side  <»f 
the  pins  made  l)y  a  cut  with  a  sharp  knife  or  ciiiseh 

Investing  and  Heating.— The  teeth  backed  and  luted  to 
tin-  base-phitc  are  removed  from  the  i)laster  cast,  invested 
with  investment  compound  to  a  tliickiK'ss  of  one-fourth  or 


396  GOLD  AS  A  BASE-PLATE 

one-half  inch.  The  investment  is  thoroughly  dried,  and 
while  warm  a  small  amount  of  flux,  rubbed  to  a  cream  or 
mixed  with  vaseline,  is  applied  to  the  joints  and  pieces  of 
fluxed  solder  placed  upon  the  joint,  also  a  small  piece  rested 
upon  each  pin  so  as  to  unite  the  pin  and  backing.  The 
invested  case  is  placed  upon  a  combined  supporter  and 
heater  (Fig.  275),  and  gradually  heated  until  it  has  attained 
a  dull  red  heat.  The  porcelain  must  be  heated  up  through 
the  investment  and  not  through  the  metal  backing.  In 
other  words,  the  porcelain  must  expand  in  advance  of  the 
metal  pins  to  avoid  cracking.  The  work  having  been 
heated  to  a  dull  red  state  is  ready  for  the  blowpipe.  The 
yellow-tinted  brush  flame  is  played  over  the  investment  and 
gradually  brought  over  upon  the  metal,  and  the  brush  flame 
continued  until  the  solder  begins  to  melt,  when  each  piece 
of  solder  is  touched  consecutively  with  the  blue  needle 
flame  and  thoroughly  flowed.  Should  any  portion  of  the 
work  require  a  large  amount  of  solder  after  the  first  tacking, 
it  is  best  done  by  feeding  into  the  flame,  held  at  the  point 
to  be  filled  with  solder,  a  long  strip  of  fluxed  solder  held  in 
clamped  tweezers.  Care  must  be  exercised  not  to  hold  the 
flame  at  one  point  long  enough  to  melt  the  work.  This  is 
accomplished  by  interrupting  the  flame  contact. 

Cooling  the  Investment. — The  fire  is  withdrawn  and  the 
case  permitted  to  stand  until  cold.  No  precaution  is  required, 
except  to  protect  from  drafts  of  air,  as  too  rapid  radiation  of 
heat  might  craze  the  porcelain.  The  investment  compound 
is  a  poor  radiator  of  heat,  therefore  retains  the  heat  and 
permits  the  metal  to  cool  in  advance  of  the  porcelain.  The 
cracking  of  porcelain  in  soldering  is  largely  due  to  expanding 
the  metal  pins  in  advance  of  the  porcelain  in  heating  up  and 
cooling  the  porcelain  in  advance  of  the  pins  in  the  cooling- 
off  process.  Hence  the  principal  time  of  danger  of  cracking 
is  while  heating  up. 

Partial  Upper  Dentures. — The  base-plate  is  designed  in 
outline  to  meet  the  requirements  of  the  case.  Modern 
thought  requires  as  little  of  the  vault  to  be  covered  with  the 
base-plate  as  is  consistent  with  strength  and  rigidity.    Fig. 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE    397 

290  shows  a  partial  gold  base-plate  fitted  about  all  of  the 
remaining  teeth.  Figs.  291  and  292  show  a  band  base-plate 
\\4th  as  little  surface  covered  as  is  consistent  with  stability. 
The  band  should  extend  across  and  in  proximity  to  the  high- 

FiG.  290 


FiQ.  291 


est  i)ortion  ol"  the  vault.  Fig.  293  shows  a  partial  dentnre 
on  a  vulcanite  base-i)hite  with  gold  clasps  that  is  a  com- 
promise between  the  two  preceding  illustrated  cases. 

Partial  gold  base-plates  may  be  constructed  by  citlici- 
the  swaged  or  cast  method.  However,  as  has  been  stated, 
the  quality  of  adaptation  is  the  only  factor  of  superiority 


398 


GOLD  AS  A  BASE-PLATE 


of  the  cast  over  the  swaged  base-plate;  and  it  is  questionable 
if  this  closeness  of  adaptation  is  desirable;  if  contact  with  a 
smooth  surface  is  not  more  acceptable  to  the  contiguous 
tissues.  As  contact  is  almost  a  negligible  factor  in  the 
retention  of  partial  base-plates,  the  contact  over  the  vault 
portion  of  the  mouth  may  be  ignored;  except  that  sufficient 
contact  must  be  had  to  prevent  the  sound  waves  of  vocali- 
zation passing  between  it  and  the  roof. 


±■10.  zyz 


Fig.  293 


Swaged. — The  model,  die  and  counter,  swaging  and 
reinforcement  have  been  considered.  Clasps  as  retainers, 
their  form,  location,  and  construction  are  discussed  in 
Chapter  VII,  but  adjusting  the  clasp  to  the  base-plate  will 
require  attention. 

The  partial  base-plate  with  all  of  its  attachments,  save 
clasps,  soldered  is  tried  upon  the  die,  and  if  found  out  of 
shape  it  is  reswaged  in  the  swager.    The  base-plate  is  then 


SOLDERING  ATTACHMENTS  TO  GOLD  BASE-PLATE    399 

pickled  and  cleansed  and  adjusted  to  the  mouth.  Should 
its  weight  be  too  great  for  its  retention  by  contact,  the 
maxillary  surface  is  moistened  and  sprinkled  with  powdered 
gum  tragacanth  and  held  in  place  for  a  moment  until  adhesion 
is  established.  A  plaster  impression  is  taken  sufficient  to 
cover  the  portions  of  the  teeth  to  be  clasped  and  the  con- 
tiguous base-plate.  Should  the  base-plate  not  leave  the 
mouth  with  the  impression,  it  is  removed  and  replaced  in 
the  impression.  Another  plaster  impression  is  taken,  neces- 
sarily of  the  teeth  to  be  clasped  only.  This  impression  may 
be  of  the  teeth  individually  or  collectively.  The  impression 
containing  the  base-plate  is  varnished  and  carefully  filled 
with  investment  compound.  The  impression  of  the  teeth 
only  is  varnished  and  filled  with  plaster  or,  preferably,  Spence 
plaster  compound.  Some  prefer  filling  this  impression  with 
bismuth  alloy,  but  nothing  is  to  be  gained  over  the  Spence 
compound  save  time,  and  there  is  danger  of  contaminating 
the  clasp  metal  with  the  base  metal  of  the  bismuth  alloy. 
The  Spence  compound  should  stand  about  an  hour  before 
taking  from  the  impression,  and  then  another  hour  or  more 
to  harden.  The  clasps  are  formed  over  the  Spence  com- 
pound casts,  as  instructed  in  Chapter  VII,  and  adjusted  upon 
the  investment  compound  cast  containing  the  base-plate. 
Contact  must  be  had  between  the  clasp  and  base-plate  either 
by  proximity  or  another  piece  of  metal  called  a  standard. 
Sometimes  two  standards  are  required  (see  Chapter  \\1). 
If  the  base-plate  is  securely  caught  in  the  investment  com- 
pound cast  and  the  clasps  are  securely  held  by  their  inherent 
elasticity,  no  further  investment  will  be  required ;  but  if 
the  parts  to  be  soldered  are  not  securely  held,  the  cast  should 
be  saturated  with  water  and  invested  with  the  spaces  for 
.soldering  as  wide  open  as  possible.  The  case  is  well  dried, 
the  joints  supplied  with  flux  and  solder,  and  heated;  rapidly 
if  desired,  as  there  are  no  porcelains  to  be  considered.  If 
the  clasp  and  base-plate  are  to  be  connected  by  a  standard 
the  upper  end  should  first  be  soldered,  as  otherwise  the 
contraction  of  the  solder  about  the  lower  end  of  the  standard 
is  liable  to  pull  it  away  from  the  clasp.    The  soldering  com- 


400 


GOLD  AS  A  BASE-PLATE 


pleted,  there  being  no  porcelains  attached,  the  case  may 
be  rapidly  cooled  by  placing  in  water.  The  metal  is  then 
pickled,  when  it  is  ready  for  the  vulcanite  superstructure. 
The  base-plate  without  porcelains  may  be  rapidly  pickled 
by  heating  nearly  to  redness  and  quenching  in  the  pickle 
bath. 

Fig.  294 


Casting. — Figs.  291  and  292  show  two  views  of  a  cast  base 
for  a  partial  upper  denture.  The  only  trouble  with  such  a 
base-plate  is  that  it  is  crystalline,  flexible,  inelastic,  unduly 
heavy,  and  destined  soon  to  be  out  of  shape.  Moral:  Bont 
depend  upon  the  casting  method  for  gold  base-plates.  A 
former  statement  will  bear  repeating.  The  casting  method 
is  unsuitable  for  full  gold  base-plates,  bands,  bars,  and 
clasps.    (The  case  shown  is  a  combination  of  cast  and  solder 


BAR  LOWER  DENTURES  401 

methods.)  It  is  suitable  for  small  saddles  which  are  to  be 
reenforced  with  vulcanite  or  soldered  attachments.  As  gold 
casting  will  be  elucidated  in  other  books  of  this  series,  it  is 
unnecessary  to  encumber  these  pages  with  that  which  has 
small  practical  bearing  upon  this  department  of  dentistry. 
However,  a  few  general  remarks  are  relevant. 

The  wax  model  base-plate  should  be  formed  as  near  like 
the  desired  finished  piece  as  possible,  thus  saving  stock  and 
labor.  Two  or  more  sprue  hole  or  feed-gate  formers  should 
be  attached  at  the  highest  elevations;  and  other  high  eleva- 
tions liable  to  form  air  pockets  should  have  vents  provided. 
(The  vents  should  not  be  provided  for  the  vacuum  method 
of  casting.)  The  feed  gates  in  size  should  be  in  direct  ratio 
to  the  size  of  the  mold  up  to  the  extent  of  practicability. 
The  fluidity  of  gold  should  be  in  direct  ratio  to  the  amount 
of  gold  to  pass  through,  a  given  size  sprue  hole.  By  what- 
ever method  the  gold  is  cast,  pressure  should  be  maintained 
until  the  gold  is  crystallized.  The  method  advocated  for 
casting  aluminum,  that  is  the  feed  gate  to  enter  at  the 
bottom  of  the  mold  is  not  applicable  for  gold,  because  of 
the  great  specific  gravity  and  the  correspondingly  small 
feed  gate  permissible.  Fig.  294  shows  a  wax  model  for  a 
saddle  base-plate  with  suitably  arranged  feed  and  vent 
sprue  formers. 

BAR  LOWER  DENTURES 

Partial  lower  dentures  may  be  made  with  a  band  of 
vulcanite  (Fig.  308)  on  the  lingual  aspect  of  the  remaining 

Fig.  295 


natural  teeth;  or  with  a  band  of  reenforced  gold  (Fig.  295); 
or  with  a  bar  as  shown  in  Fig.  298.    The  bar  has  the  merit 
26 


402  GOLD  AS  A  BASE-PLATE 

of  being  less  cumbrous  and  interfering  with  the  adjacent 
tissues  the  least  of  any  method  yet  devised.  The  method 
is  growing  in  popularity  with  both  patient  and  practitioner. 

Technique. — The  saddles  may  be  made  of  either  swaged  or 
cast  gold.  (There  is  probably  no  place  where  the  cast  base 
is  as  applicable  as  for  these  cases.)  In  either  case  the  bar 
should  be  made  of  clasp  gold  wire  soldered  to  the  saddles; 
after  which  the  clasps  should  be  formed  and  soldered  to  the 
saddles.  As  the  bar  with  vulcanite  saddles  are  the  most 
commonly  made,  its  tcv^hnique  will  be  sufficient  for  the 
method,  as  the  slight  mofiification  required  for  the  metal 
saddles  will  suggest  itself  to  any  workman's  mind. 

Material. — No.  12  B.  &  S  gauged  clasp  gold  wire  is  the 
material  used.  Should  it  be  apparent  that  unusual  strength 
will  be  required,  No.  11  gauged  wire  may  be  substituted, 
or  two  wires  of  No.  15  or  16  gauge,  soldered  one  above  the 
other,  will  serve  well  the  purpose. 

Single  Wire  Method. — A  plaster  impression  is  taken  and  a 
Spence  Compound  cast  obtained.  (Care  should  be  exercised 
not  to  deface  this  cast,  as  it  is  the  only  one  required  to 
complete  the  denture.)  Retaining  clasps  are  fitted  to  the 
teeth  to  be  clasped.  A  line  is  marked  upon  the  lingual 
aspect  of  the  cast  to  indicate  the  position  of  the  lower  edge 
of  the  bar.  The  bar  must  be  kept  high  enough  not  to  inter- 
fere with  the  frenum  lingua  or  other  soft  tissues  of  the  floor 
of  the  mouth.  A  roll  of  soft  wax  is  conformed  to  the  cast 
so  that  its  upper  surface  will  form  a  ledge  parallel  with  the 
line  marked  for  the  bar.  This  ledge  of  wax  is  for  convenience 
in  shaping  and  supporting  the  bar.  A  bar,  sufficiently  long 
to  extend  at  least  one-half  inch  into  each  saddle,  is  annealed 
by  heating  to  a  dull  cherry-red  and  quenching  in  water. 
This  is  bent  with  the  fingers  and  a  pair  of  pliers  having  one 
oval-faced  beak.  The  bending  is  continued  until  the  bar 
rests  upon  the  edge  of  wax  and  is  from  3^2  to  yV  of  an  inch 
from  the  cast.  If  the  wire  is  nearer  the  soft  tissue  than  3^2" 
of  an  inch  there  is  much  danger  that  it  will  in  time  become  a 
source  of  irritation.  The  bar  and  clasps  are  removed  and  the 
cast  is  painted  with  liquid  silex  above  the  wax  ledge  and  for 


BAR  LOWER   DENTURES 


403 


half  an  inch  be>ond  the  clasped  teeth.  The  clasps  are  then 
replaced  with  just  enough  tension  to  hold  them  securely, 
and  the  bar  set  in  ])lace  uj)on  the  ledge  of  wax.  The  clasps 
and  bar  are  then  luted  together  with  a  batter  of  quick- 
setting  plaster,  the  plaster  extending  from  one  clasped  tooth 
to  the  other.    The  plaster  luting  should  rest  upon  the  lingual 


Fi<i.   290 


Fig.   297 


aspect  of  the  intervening  teeth  only  to  give  body  to  the  lute. 
\Nhen  the  luting  plaster  has  become  hard  and  strong,  it  is 
removerl  from  the  cast.  It  will  hold  the  bar  and  probably 
both  clasps.  Ilowev^er,  should  any  one  or  all  three  of  the 
|>ieces  of  metal  be  parted  from  the  luting  they  are  easily 
replaced  and   fastened   with   a  little  wax.     Fig.  290  shows 


404 


GOLD  AS  A  BASE-PLATE 


the  luting  plaster  with  the  clasps  waxed  in  place.  The  plaster 
luting  is  varnished  with  shellac  and  sandarac  and  covered 
with  investment  so  as  thoroughly  to  hold  and  support  the 
bar  and  clasps.    Fig.  297  shows  such  an  investment  with  the 


Fig.  298 

■P 

'^^m 

n 

■ 

^^P'-^  m 

WK^w 

n 

*>• 

J 

Fig.  299 


luting  plaster  cut  away  and  the  clasps  and  bar  united  with 
standards.  Fig.  298  shows  the  same  case  removed  from  the 
investment  and  placed  upon  the  Spence  compound  cast. 
The  remainder  of  the  work  of  construction  is  vulcanitework, 
and  should  need  no  further  description. 


SOME  PRACTICAL  CASES 


405 


Double  Wire  Method. — Fig.  299  shows  the  two  wires  of 
No.  IG  gauge  united  with  wax.  They  are  removed  and 
invested  as  shown  in  Fig.  300,  soldered  together  with  18  k 
or  20  k  solder.  This  bar  is  then  luted  with  plaster  to  the 
clasps  and  soldered  as  previously  described. 

Fig.  300 


Too  Close  Fitting  Bar. — Dr.  S.  Marshall  Weaver  describes 
a  method  for  bending  back  the  bar  when  unfortunately  it 
presses  into  the  soft  tissues.  A  little  wax  is  melted  upon  the 
bar  opposite  the  impingement.  The  denture  is  then  invested 
in  Spence  compound  heavily  covering  all  but  the  portion  of 
wire  opposite  the  wax  or  that  portion  impinging  upon  the 
soft  tissues.  WTien  the  Spence  compound  is  thoroughly 
hard  the  bar  is  bent  into  the  space  formed  by  the  wax,  with 
a  punch  and  mallet. 


SOME  PRACTICAL  CASES 


A  few  practical  cases  will  offer  suggestions  to  the  student 
for  improvising  gold  attachments  for  special  cases. 

Fig.  1:501  shows  a  cast  with  clasps  attached.  Fig.  302,  the 
same  case  waxed  ready  for  flasking.  Fig,  293  is  the  finished 
piece. 

Fig.  303  shows  a  partial  upper  to  supply  the  teeth  distal 
to  the  cuspid  on  one  side  of  the  mouth,  with  all  the  remaining 


406 


GOLD  AS  A  BASE-PLATE 


upper  teeth  closel}"  articulated  (knuckled) .    It  was  necessary 
to  clasp  the  cuspid,  carrying  it  slightly  under  the  gum,  as 


Fig.  301 


that  was  the  only  way  of  getting  a  grip  on  the  tooth;  besides, 
the  natural  gum  was  exposed  when  laughing,  necessitating 


SOME  PRACTICAL  CASES 


io: 


the  clasp  being  accurately  fitted  and  appearing  as  a  cer\'ical 
filling.  The  attachment  for  the  other  side  of  the  mouth 
consisted  of  a  crib  formed  by  fitting  a  piece  of  clasp  gold 
plate  upon  both  the  buccal  and  lingual  surfaces  of  the  first 
and  second  molars,  and  these  joined  with  a  U-shaped  staple 


Fig.  303 


Fig.  304 


of  half-round  1 1 -gauged  clasp  gold  wire  resting  in  the  groove 
between  the  molars. 

Fig.  304  is  a  bar  lower  for  the  same  mouth.  The  teeth  are 
missing  from  the  cuspid  backward  on  the  opposite  side  of 
the  mouth  from  the  upjK'r  shown  above.  This  case  required 
a  clasp  upon  the  cuspid,  but  fortunately  there  was  a  space 


408 


GOLD  AS  A  BASE-PLATE 


between  the  second  bicuspid  and  molar,  so  the  crib  was 
formed  with  a  clasp  upon  both  the  bicuspid  and  the  molar, 
with  a  lug  resting  upon  the  occlusal  surface  of  the  molar. 

Fig.  305  shows  the  two  central  incisors  with  two  staple 
cribs. 


Fig.  305 


Fig.  306  shows  crib  and  clasp  ready  for  constructing  a 
vulcanite  denture.  These  cribs  were  necessary  because 
attachment  had  to  be  made  to  a  fixed  bridge. 


Fig. 

306 

HP" 

"^ 

H| 

■| 

Hi 

BVH 

^^^iL. 

1 

i 

1 

■i^^m 

^E     f^^^B 

^^mc-:Wt^ 

"^•^R 

'^1 

IP 

.-.^H 

1 

1 

1 

^ 

J 

Fig.  307  shows  a  partial  lower  case  with  gold  clasps 
carrying  three  natural  lower  incisors.  This  method  is 
possible  when  the  teeth  are  recently  extracted  and  free  from 


SOME  PRACTICAL  CASES 


409 


decay.  Teeth  used  by  this  method  are  usually  those  lost 
by  pyorrheal  conditions.  The  natural  teeth  must  not  be 
put  through  the  vulcanizer,  as  the  heat  and  sulphur  will 
completely  disintegrate  them.  The  tooth  or  teeth  are  cut 
off  the  desired  length  to  fill  the  space  and  the  pulp  chambers 
enlarged  to  loosely  admit  a  16-gauged  clasp  gold  wire.  If 
the  tooth  is  to  be  attached  to  a  gold  base-plate,  the  wire 
should  be  aligned  and  soldered  to  the  base-plate  and  the  tooth 

Fig.  307 


Fig.  308 


cemented  to  the  pin  with  oxyphosphate  of  zinc.  If  the  teeth, 
as  in  this  case,  are  to  be  attached  to  a  vulcanite  base-plate, 
a  small  piece  of  gold  plate  is  soldered  upon  the  end  of  each 
of  the  posts.  The  cervical  end  of  the  teeth  are  wet  with 
water,  placed  upon  the  posts,  and  embedded  and  aligned  in 
the  sf)ftened  wax.  The  wax  is  conformed  and  smoothed 
about  the  teeth,  which  are  lifted  off  the  posts,  and  the  case 
completed  in  vulcanite.  Fig.  308  shows  the  vulcanite  base- 
|)Iate  ready  for  cementing  the  teeth. 


410 


GOLD  AS  A  BASE-PLATE 


Fig.  309  illustrates  the  metal  portion  of  a  bar  lower  with 
a  cast  shoe  for  the  left  bicuspids  and  molars,  a  half  cope 
for  the  right  second  bicuspid,  and  spring  clasps  for  the  right 
second  bicuspid,  left  second  bicuspid,  and  left  second  molar. 
A  tang  is  also  shown  for  attaching  the  missing  incisors. 


Fig. 

309 

ppV 

■1 

PI 

^■m 

^ 

M^^k 

Fig.  310 


Fig.  310  is  a  bar  lower  having  two  incisors  attached  with 
vulcanite  to  a  tang.  It  may  be  seen  that  the  attachment 
to  the  right  second  bicuspid  consists  of  a  cope  and  spring 
clasp. 

Fig.  311  has  a  cast  ferrule  telescoping  three  crowned  teeth. 

Fig.  312  illustrates  the  method  of  reenforcing  the  tang  of 


REPAIRING  GOLD  PLATE  WORK 


411 


the  clasp.  The  tang  is  attached  to  the  clasp,  as  shown  in 
Fig.  184,  and  then  conformed  to  the  cast.  It  is  removed  from 
the  cast,  supported  upon  the  magnesia  soldering  block,  and 


the  reenforcement  of  wire  or  a  piece  of  scrap  gold  plate 
soldered  on.  This  reenforcement  is  necessary  to  prevent 
the  clasp  (in  time)  breaking  from  the  tang. 


REPAIRING    GOLD    PLATE    WORK 

If  the  denture  to  be  repaired  is  soldered  work  only,  it  is 
simply  repaired.  If  it  is  combination  work  of  gold  and 
vulcanite  and  the  gold   is  broken   it  will  be  necessary  to 


412  GOLD  AS  A  BASE-PLATE 

remove  the  vulcanite,  solder  and  rebuild  the  vulcanite 
portion.  If  it  is  a  clasp  broken,  which  often  happens,  it 
may  usually  be  repaired  by  fitting  another  clasp  to  the 
tooth,  soldering  a  lug  to  it  to  fit  into  a  filed  groove  in  the 
contiguous  vulcanite,  and  attaching  with  vulcanite. 


CHAPTER    XII 

TIN  AS  A  BASE-PLATE 

The  cheoplastic  or  tin  method  for  forming  base-plates  was 
given  to  the  profession  about  1855  by  Dr.  A.  A.  Blandy. 
Recognizing  that  a  casting  process  would  provide  the  most 
perfect  adaptation,  and  that  pure  tin  was  an  acceptable 
metal  to  the  tissues,  the  profession  readily  accepted  the 
method.  The  later  methods  have  been  somew^hat  more 
simple  than  the  earlier  one. 

The  metal  consists  of  tin  alloyed  wnth  such  metals  as 
bismuth,  silver,  gold,  and  possibly  cadmium  and  antimony. 
Several  of  the  alloys  on  the  market  were  proprietary^  and 
their  composition  not  published.  The  formulas  of  the 
pubUshed  ones  are: 

Kingsley's  alloy:  Tin,  16  ounces;  bismuth,  1  ounce. 

Reese's  alloy:  Tin,  20  parts;  gold,  1  part;  silver,  2  parts. 

Bean's  alloy:  Tin,  95  parts;  silver,  5  parts. 

Watt's  and  Weston's  alloys,  proprietary  preparations,  are 
the  principal  ones  on  the  market.  These  are  both  low  fusing 
('about  400°  F.)  and  interchangeable  in  manipulation.  The 
method  is  mostly  confined  to  lower  dentures.  Since  the 
introduction  of  successful  casting  of  pure  aluminum  there 
will  be  less  occasion  for  its  use.  As  the  aluminum  casting 
is  better  understood,  it  should  entirely  supersede  the  tin 
alloys,  as  it  is  much  stronger,  more  cleanly  and  durable  than 
the  tin  alloys. 

Technique. — The  same  investment  compound  used  for 
casting  alumirmm  serves  for  the  tin  alloys.  The  necessary 
implements  are  a  Watt's  flask  (Fig.  'M'S)  and  a  ladle  or  large 
spoon. 

The  wax  model  is  formed  the  same  as  for  an  aluminum 
base-plate,  flasked  in  the  first  half  of  the  flask  (Fig.  314), 


414 


TIN  AS  A   BASE-PLATE 


paying  no  attention  to  the  gates  B  and  C  at  this  time;  and 
when  the  investment  is  hard,  varnish  and  fill  the  second 
half,  having  the  wax  model  wet  and  jarring  the  investment 
compound  well  into  place.  The  flask  is  opened  the  same  as 
a  vulcanite  flask  (Chapter  VI)  and  wax  removed.  The 
investment  material  is  removed  from  the  funnels  and  a  small 
and  large  gate  cut  as  shown  at  B  and  C  respectively.  The 
two  sections  of  the  flask  are  placed  over  a  piece  of  sheetiron 


on  the  gas  stove  and  dried  until  no  steam  is  given  off.  They 
are  then  bolted  together,  and  an  ingot  of  the  tin  alloy  melted 
in  the  ladle  or  spoon  over  a  Bunsen  burner  and  poured  into 
the  large  gate  until  the  metal  appears  at  the  small  gate. 
Should  there  be  any  bubbling  the  flask  should  be  grasped 
by  the  handle  and  slightly  jarred  against  the  bench  until 
the  bubbling  ceases.  The  casting  should  stand  until  it  is 
cold,  and  then  be  opened.     However,  after  the  metal  has 


TIN  AS  A  BASE-PLATE 


415 


partially  cooled,  it  may  be  placed  in  cold  water  and  the 
cooling  expedited.     The  sprues  are  cut  from  the  casting 


Fig.  314 


with  a  mechanical  saw,  and  the  filling  done  with  a  vulcanite 
nie.    It  IS  polished  the  same  as  vulcanite. 


CHAPTER    XIII 

CONTINUOUS  GUM  DENTURES 

By  this  term  is  meant  a  base-plate  of  platinum,  the  outer 
surface  of  which  is  covered  with  a  continuous  layer  of 
porcelain. 

It  is  true,  the  term  might  equally  well,  or  better,  be  applied 
to  vulcanite  or  celluloid;  but  the  term  was  applied  to  the 
enamelled  platinum  before  the  introduction  of  the  other 
materials,  and  is  universally  accepted  as  applicable  to  the 
enamelled  platinum  only;  therefore,  to  call  any  other 
material  by  this  name  is  a  manifest  deception. 

The  French  were  the  earliest  experimenters  in  porcelain 
work  for  artificial  dentures;  but  it  remained  for  Dr.  John 
Allen,  of  Cincinnati,  and  later  of  New  York  City,  to  perfect 
the  material  and  method  of  construction.  He  perfected  the 
process  in  1846.  The  furnace  work  of  the  early  days  was 
difficult  and  hazardous.  Within  a  decade  of  the  invention 
of  continuous  gum  work  vulcanite  was  placed  before  the 
profession.  Because  of  its  inexpensiveness  and  ease  of 
construction  it  nearly  drove  the  more  expensive  and  better 
methods  from  the  field.  However,  in  the  last  quarter  of  a 
century  the  facilities  for  constructing  dentures  of  the  better 
quality  have  been  so  much  improved  that  they  are  gradually 
coming  into  their  own.  So  much  so  that  any  student  who 
is  desirous  of  equipping  himself  for  practice  among  the  better 
class  of  patients  should  be  thoroughly  conversant  with  the 
construction  and  merits  of  continuous  gum  dentures.  It  is 
without  doubt  the  most  cleanly,  healthful,  and  esthetic  of 
any  material  or  denture  placed  in  the  mouth.  It  is  composed 
of  mineral  matter  only  and  these  of  the  greatest  purity  and 
compatibility  to  the  human  economy.  The  materials 
entering  into  its  composition  are  platinum,  iridium,  gold, 
and  high-fusing  porcelain. 


EQUIPMENT 


417 


Porcelain. — Porcelain  suitable  for  this  work  is  procurable 
at  the  supply  houses.  It  is  known  as  "Continuous  Gum 
Body"  and  "Gum  Enamel."  The  body  is  in  boxes  contain- 
ing one  ounce  each,  and  the  enamel  one-half  ounce  to  the 
box.     Close's  product  (modified  Allen  formulas)  is  the  one 

Fig.  315 


most  commonly  used.  The  body  fuses  at  2300°  F.,  and  the 
enamel  about  100°  lower.  They  are  of  the  same  composition, 
with  mon;  flux,  as  porcelain  teeth. 

Equipment. — For  an  office  equipped  for  gold  work  nothing 
is  required  except  a  furnace  for  baking  the  porcelain.     If 
27 


418 


CONTINUOUS  GUM  DENTURES 


the  electric  current  is  to  be  had,  one  of  the  various  electric 
furnaces  upon  the  market  is  to  be  preferred;  otherwise  a 
gasoline  burning  furnace,  of  which  there  are  several  makes. 

To  Dr.  L,  E.  Custer,  of  Dayton,  Ohio,  belongs  the  credit 
of  inventing  and  demonstrating  the  first  dental  electric 
furnace.  His  first  demonstration  was  before  the  Ohio  State 
Dental  Society,  in  1894.     Since  that  date  other  furnaces 

Fig.  316 


possessing  excellent  features  have  been  invented,  but  none 
have  surpassed  the  Custer  furnace  in  scientific  construction. 
Fig.  315  shows  the  furnace  and  illustrates  the  method  of 
wiring  so  as  to  produce  an  economical  and  evenly  distributed 
heat. 

An  auxiliary  instrument  to  the  furnace  is  the  pyrometer. 
To  Dr.  Weston  A.  Price,  of  Cleveland,  belongs  the  credit  of 
adapting  this  instrument  to  the  dental  furnace.     Fig.  316 


EQUIPMENT 


419 


shows  the  Price  furnace  and  jnrometer  complete.  The 
instrument  is  the  thermopile  adapted  to  this  special  use,  and 
requires  little  experience  to  fuse  the  porcelain  well;  however, 
judgment  must  be  exercised  even  with  this  perfect  instru- 
ment. Without  the  pyrometer  the  operator  must  depend 
upon  his  eye  to  determine  the  heat.  Either  with  or  Avithout 
the  pyrometer  the  operator  must  have  a  definite  method  of 
manipulating  the  rheostat,  and  use  judgment.    The  voltage 

Fig.  317 


of  any  current  varies  within  certain  limits,  which  will  have 
an  influence  indicated  by  the  pyrometer,  and  in  connection 
with  the  rheostat  can  be  better  controlled  than  by  the  eye. 
Xevcrthcless,  an  operator  of  average  discernment  and 
ability  should,  with  a  little  experience,  be  able  to  produce 
excellent  results  with  an  electric  furnace,  either  with  or 
without  the  pyrometer. 

Fig.  317  shows  one  f)f  the  gasoline  furnaces. 


420  CONTINUOUS  GUM  DENTURES 


TECHNIQUE  OF  CONSTRUCTION 

Plaster  impression,  cast,  model,  die,  and  counter-die  are 
required,  the  same  as  for  a  full  gold  denture. 

A  base-plate  of  pure  platinum  32-gauged  (B.  &  S.)  is 
formed.  Care  should  be  taken  (well-oiled  die  and  counter) 
not  to  contaminate  the  platinum  with  base  metal.  The 
base-plate  swaged  and  trimmed  is  tried  in  the  mouth  and 
tested  for  palatal  length,  and  freedom  from  impingement 
upon  the  muscle  attachments.  The  peripheral  border 
perfected  and  the  adaptation  inspected,  it  is  returned  to  the 
die  for  forming  a  reenforcing  piece  for  the  palatal  border. 
Should  the  adaptation  not  be  satisfactory,  it  must  be 
corrected,  at  this  stage  of  construction,  even  to  the  extent, 
if  necessary,  of  obtaining  a  new  impression  and  constructing 
a  new  die  and  counter. 

The  palatal  reenforcement  should  be  i  of  an  inch  wide  in 
the  median  line  and  slightly  taper  toward  and  terminate  at 
the  tuberosities  (Figs.  321  and  328).  This  doubler  is  swaged 
of  30-gauged  (B.  &  S.)  pure  platinum.  After  being  swaged 
it  is  placed  upon  the  base-plate  and  swaged.  The  anterior 
border  of  the  doubler  is  turned  up  with  pliers  at  an  angle 
of  45  degrees  so  that  in  the  finished  piece  the  porcelain  will 
be  engaged  under  this  edge  of  the  doubler.  The  doubler 
will  be  distorted  in  bending  the  edge;  this  is  corrected  by 
wiping,  pickling,  annealing,  and  burnishing  the  doubler 
to  the  base-plate.  The  bending  and  burnishing  are  alter- 
nated until  suitable  adjustment  is  obtained.  The  base-plate 
and  doubler  are  cleansed  and  clamped  together  with  wire 
clamps,  pure  gold,  35-gauged,  cut  in  small  pieces,  is  placed, 
without  flux,  under  the  turned  edge  and  melted  with  the 
blowpipe  so  as  to  draw  the  gold  as  solder  outward  and 
perfectly  attach  the  doubler  to  the  base-plate.  An  18- 
gauged  iridioplatinum  wire  is  soldered  with  35-gauged  pure 
gold  to  the  periphery  of  the  plate,  from  tuberosity  to  tuber- 
osity, in  the  same  manner  as  wiring  a  gold  plate.  The 
charcoal  soldering  block  should  not  be  used,  as  carbon  is 


TECHNIQUE  OF  CONSTRUCTION  421 

detrimental  to  platinum.  The  magnesia  or  abestos  block 
will  serve  the  purpose.  Flux  is  unnecessary  as  a  cleanser,  as 
noble  metals  only  are  used;  but  it  may  serve  to  hold  the 
solder  in  place.  No  more  gold  should  be  used  in  continuous 
gum  dentures  than  is  necessary  to  unite  closely  jfitted 
joints.  Some  advocate  the  use  of  platinum  solder  (gold 
with  20  or  25  per  cent,  of  platinum)  and  the  oxyhydrogen 
blow^pipe  for  soldering  platinum  for  continuous  gum  den- 
tures. This  is  quite  unnecessary,  as  the  pure  gold  will  alloy 
with  the  platinum  base-plate  while  baking  the  porcelain; 
however,  close-fitting  joints  are  necessary,  probably  more 
so  with  pure  gold  used  as  solder  than  with  platinum  solder. 

Fig,  31S 


The  reenforced  platinum  base-plate  is  used  in  obtaining 
the  wax  occlusion  and  contour  models;  and  mounting  upon 
the  antagonizor.  Teeth  suitable  for  the  case  (Figs.  205 
and  318)  are  selected  and  mounted  in  wax.  The  case  is 
ready  for  trial  in  the  mouth.  It  should  be  inspected  for 
adaptation,  contour,  and  cosmetic  effects,  which  being 
satisfactory,  the  case  is  ready  for  soldering  the  teeth  to 
the  base-plate. 

Soldering  the  Teeth. — It  is  quite  essential  that  the  waxed 
trial  denture  slH>uld  be  well  contoured  to  develop  all  the 
restorations  required.    A  record  is  made  of  the  thickness  of 


422  CONTINUOUS  GUM  DENTURES 

the  gum  portion  at  the  median  hhe,  at  the  centre  of  each 
cuspid  eminence,  and  of  the  buccal  contours  (if  any  are 
required)  by  measuring  with  cahpers  and  making  indicative 
marks  on  paper.  The  wax  is  cut  away  with  a  warmed  wax 
knife,  from  the  labial  and  buccal  surfaces,  leaving  the  wax 
on  the  lingual  surface  intact  to  support  the  teeth  while 
investing  (Fig.  319). 

Fig.  319 


An  investment  suitable  for  this  work  is  composed  of  any 
coarse  silica  compound  and  approximately  one-fifth  of  its 
bulk  of  asbestos;  either  the  long  fiber  or  the  short  (tenax) 
fiber  may  be  used.  A  soft  iron  wire  ring  of  15  gauge  is 
formed  to  place  about  the  denture  in  its  largest  plane  and 
be  free  of  contact  by  i  of  an  inch  at  every  point.  A  sufficient 
quantity  (half-bowlful)  of  investment  is  wet  up  to  a  soft 
putty  consistency.  The  intaglio  of  the  denture  is  filled  and 
a  portion  quickly  spread  over  the  labial  and  buccal  surfaces 
of  the  teeth;  the  balance  of  the  investment  is  spread  on  the 
flat  surface,  upon  which  plaster  casts  are  formed;  the  partially 
invested  case,  with  its  exposed  surface  upward,  is  pressed 
into  it  so  that  the  most  prominent  points  are  covered  by  at 
least  i  of  an  inch;  the  wire  ring  is  placed  about  opposite 
the  cervical  portion  of  the  teeth;  and  the  spatula  used  to 


TECHNIQUE  OF  CONSTRUCTION  423 

draw  the  spread-out  investment  up  over  the  wire  ring  and 
the  morsal  ends  of  the  teeth,  so  that  all  will  be  strongly 
covered.  The  wire  serves  two  purposes,  as  a  strengthener 
and  as  a  guide  to  thickness.  When  the  investment  is  hard 
it  is  set  in  a  warm  place  to  dry  and  soften  the  wax,  which 
is  picked  out  and  the  pins  of  the  teeth  bent  upward.  Fig. 
320  shows  the  invested  case  with  the  lingual  surface  of  the 
base-plate  and  the  teeth  exposed ;  also  some  of  the  pins  are 
seen  bent  upward. 

Fig.  320 


j<f^tJ^.'-~ 


Reenforcing  Wires.  —  A  12-gauged  iridioplatinum  wire  is 
bent  to  fit  closely  under  the  pins  of  the  teeth  and  with  the 
ends  in  contact  with  the  tuberosities.  The  long  platinum 
pins  of  the  teeth  are  bent  around  the  reenforcement  wire, 
thus  holding  it  securely  in  place.  The  ends  of  a  truss  wire, 
of  iridioplatinum  18-gauged,  is  placed  in  contact  with  the 
reenforcing  wire  in  the  proximity  of  the  cuspids,  and  with 
its  centre  resting  upon  the  base-plate  in  the  median  line 


424 


CONTINUOUS  GUM  DENTURES 


near  the  crest  of  the  alveolar  ridge.  A  small  piece  of  pure 
gold  (for  solder)  is  placed  at  each  point  of  contact  of  the 
wires,  pins,  and  base-plate.  The  case  is  heated  up  to  bright 
redness,  when  the  gold  is  thoroughly  fused  with  the  needle 
flame  of  blowpipe.     Figs  321   and  322  show  two  views  of 


Fig.  321 


Fig.  322 


the  case,  soldered  and  removed  from  the  investment;  thus 
giving  a  better  idea  of  the  palatal  reenforcement,  peripheral 
finishing  wire,  lingual  reenforcement,  and  truss  wires  as 
soldered  together.  The  case  should  be  tried  upon  the  die, 
and  if  warped  it  must  be  readjusted  by  pressure  with  the 


TECHNIQUE  OF  CONSTRUCTION 


425 


fingers,  and  bj^  the  aid  of  the  horn  mallet,  copper  hammer, 
and  plate  bm'nisher.    However,  if  the  case  has  been  properly 


Fig.  323 


426  CONTINUOUS  GUM  DENTURES 

handled  there  should  be  no  warpage.  The  skeleton  denture 
is  cleansed  with  a  laboratory  plate  brush  and  water.  It  is 
placed  upon  the  antagonizor  for  assurance  that  the  teeth  are 
in  proper  occlusion. 

It  is  apparent  that  the  peculiar  formation  of  the  porcelain, 
teeth,  designed  for  continuous  gum  dentures,  is  for  a  purpose. 
The  single  long  pin  is  to  furnish  a  flexible  attachment,  and 
the  root  portion  of  the  artificial  tooth  is  to  provide  contact 
with  the  base-plate;  also  as  an  aid  in  contouring,  and  in 
controlling  the  shrinkage  during  the  enamelling.  When 
testing  the  occlusion,  if  any  of  the  teeth  are  found  misplaced, 
they  may  be  brought  into  position  by  bending  the  platinum 
pins,  although  soldered  to  the  reenforcement  wire.  At  the 
same  time  the  root  portion  of  the  tooth  should  be  in  contact 
with  the  base-plate;  nevertheless,  if  either  end  of  the  tooth 
is  to  be  out  of  the  ideal  position,  it  should  not  be  the  morsal 
end.  Fig.  323  shows  a  case  wherein  the  apices  could  not  be 
in  contact  with  the  base-plate,  and  Fig.  324  shows  the 
occlusion. 

APPLYING  THE  PORCELAIN 

Body. — A  portion  of  continuous  gum  body  (about  one- 
fourth  ounce)  is  saturated  with  water  to  the  consistency  of 
stiff  mud,  and  a  portion  applied  with  a  thin  spatula  to  the 
base-plate  about  the  apices  of  the  teeth.  The  case  is  lightly 
held  by  the  index  finger  and  thumb  of  the  left  hand,  and  the 
body  jarred  and  settled  into  place  by  tapping  with  a  light 
instrument  upon  the  periphery  of  the  base-plate.  More 
body  is  added  and  jarred  until  all  space  between  the  base- 
plate, reenforcement  wire,  and  teeth  is  compactly  filled. 
The  excess  moisture  upon  the  surface,  after  each  jarring, 
is  absorbed  with  a  napkin.  The  buccal,  labial,  -and  lingual 
surfaces  are  covered  with  the  body;  a  portion  at  a  time  is 
covered  with  the  napkin  and  compressed  between  the  thumb 
and  finger,  the  finger  in  apposition  to  the  maxillary  surface. 
Care  should  be  exercised  that  no  portion  is  more  thickly 
covered  than  is  desired  for  the  completed  denture,  and  no 


APPLY  I XG  THE  PORCELAIN 


427 


attempt  should  be  made  at  contour.  Any  body  material 
upon  the  base-plate  or  teeth  when  not  required  must  be 
removed.  A  pointed  thin  blade  spatula  and  a  small  ox-hair 
brush  will  be  useful,  also  an  artist's  medium  small  pencil 
brush  moistened  and  drawn  to  a  point  (between  the  lips)  is 
useful  in  making  a  clean  cut  gum  outline. 

Fig.   325 


Fig.  .326 


Controlling  Shrinkage.  As  j^orcelain  shrinks  about  one- 
sixtli  (jf  its  volnnie  in  fusing,  it  must  be  controlled,  or  the 
teeth  will  be  drawn  out  of  place.     It  is  controlled  by  slitting 


428  CONTINUOUS  GUM  DENTURES 

the  body  so  that  it  will  draw  about  j5xed  centres.  This  is 
done  with  a  thin  spatula,  cutting  entirely  through  the  body 
to  the  base-plate,  thus  making  each  tooth  a  fixed  centre. 
Fig.  325  shows  the  Ungual  surface  slit.  Fig.  326  shows  the 
large  spaces  formed  on  the  buccal  surface  by  the  slitting, 
and  shrinkage  in  baking. 

First  Baking. — With  a  Custer  furnace,  the  case  is  placed 
in  the  furnace  with  the  teeth  upward.  The  lever  of  the 
rheostat  is  advanced  one  stop  and  the  case  given  ten  minutes 
to  dry,  after  which  the  lever  is  advanced  two  stops  every  five 
minutes,  and  upon  the  last  stop  it  is  left  for  one  to  ten  min- 
utes, as  may  be  necessary  to  produce  the  "biscuit"  bake; 
that  is,  granulated  with  a  very  slight  glazed  appearance.. 
The  time  will  vary  with  the  condition  of  the  current  and  the 
number  of  times  the  furnace  is  opened  for  inspection.  If  a 
pyrometer  is  being  used  the  lever  must  be  advanced  to  bring 
the  heat  to  the  desired  temperature  in  a  given  time,  which 
should  be  established  for  each  current  supply  and  furnace. 
Every  make  of  furnace  will  furnish  instructions  for  use.  The 
current  is  turned  off  and  the  furnace  opened  for  a  minute  or 
two  to  stop  the  fusing,  when  it  is  closed  until  cold.  The 
denture  is  placed  upon  the  cast,  and  if  warped  it  must  be 
corrected.  The  anterior  edge  of  the  palatal  reenforcement 
is  burnished  down.    Checking  of  the  body  does  no  harm. 

Second  Body. — The  case,  being  cold,  is  wet  and  body 
applied  to  fill  all  spaces  caused  by  shrinkage,  jarred,  and 
excess  moisture  absorbed  with  the  napkin.  Body  is  then 
added  to  form  all  contours.  The  crest  of  each  eminence 
should  be  the  full  thickness  of  its  corresponding  caliper 
record,  for  the  shrinkage  will  provide  space  for  the  glazing 
enamel.  Any  large  restoration  will  require  exaggerated 
body  additions,  as  the  shrinkage  will  be  greater  than  the 
enamel  added. 

Second  Baking. — ^The  case  is  placed  in  the  furnace,  dried, 
and  heated  up  the  same  as  the  first  time,  but  carried  to  a 
higher  degree  of  fusion  than  the  first  time  (probably  about 
50°  F.  higher).  The  fusion  is  checked,  and  furnace  closed 
until  cold. 


APPLYING  THE  PORCELAIN  429 

The  case  is  examined  for  shrinkage;  if  there  are  small 
shrinkage  spaces  only  they  are  filled  in  with  body  and  not 
baked,  but  if  there  are  large  crevices  the  case  should  be 
baked  again  at  about  the  temperature  of  the  first  bake. 

Enamelling. — ^As  all  contours,  including  gum  margin, 
festoons,  and  rugae,  with  their  corresponding  depressions, 
were  developed  in  the  second  coat  of  body,  it  is  necessary  only 
to  place  over  the  surface  a  smooth  layer  of  gum  enamel 
to  produce  the  light  and  dark  shading  characteristic  of 
artistically  constructed  continuous  gum  dentures.  The 
entire  surface  of  the  body  should  be  covered  with  the  gum 
enamel  wet  with  water  and  smoothed  with  an  oval-faced 
burnisher.  The  gum  margin  must  be  neatly  pencilled  and 
all  granules  of  the  gum  material  removed  from  the  teeth. 

Third  Baking. — Ordinarily  two  bakings  only  will  be 
required  for  the  body  and  one  for  the  enamel.  The  enamel 
coat  should  be  heated  up  with  the  same  care  as  the  body 
and  fused  until  the  surface  has  a  "watery"  appearance  when 
looked  at,  across  the  surface,  in  the  hot  furnace.  The  furnace 
is  opened  long  enough  to  stop  the  fusion,  closed,  and  left 
until  cold. 

Fig.  327 


Polishing. — The  porcelain  will  come  from  the  furnace 
with  a  jjcrfcct  polish,  but  the  platinum  may  be  bufi'ed  with 
the  f(;lt  biiflVr  and  pumice,  and  glossed  either  with  the  soft 
brush  wh('(.'i  and  whiting,  or  burnished.  Kigs.  327  and  328 
show  the  completed  work. 


430 


CONTINUOUS  GUM  DENTURES 

Fig.  328 


REPAIRING 

Continuous  gum  work  lends  itself  to  the  most  perfect 
repair  of  any  artificial  denture.  It  must  be  first  burned  out, 
that  is,  scrubbed  with  soap  and  water,  invested  completely 
in  the  silica-asbestos  compound,  heated  up  gradually  to  a 
high  red  heat  so  as  to  remove  all  organic  matter;  when  new 
material  may  be  added  and  fused  securely  to  the  old. 

A  broken  tooth  may  be  repaired  by  building  up  with  any 
of  the  high  fusing  enamels  used  in  inlay  work,  or  by  grinding 
out  the  remains  of  the  tooth,  setting  in  either  a  continuous 
gum  or  vulcanite  tooth  packed  with  body  and  baked;  gum 
enamelled  and  baked.  At  all  bakings  the  same  attention 
(as  described)  should  be  given  to  heating  and  tempering 
(cooling)  the  porcelain. 

Cracks  are  repaired  by  placing  on  a  cast,  chipping  off  the 
porcelain  about  the  crevice,  then  fill  and  bake. 


CHAPTER    XIV 
INTERDENTAL  SPLINTS 

Ax  interdental  splint  is  an  jy^pliance  made  of  either  metal 
or  vulcanite  and  placed  between  the  jaws  to  support  a 
fracture  of  either  or  both  the  maxillse  and  mandible. 

Interdental  splints  in  conjunction  with  submental  com- 
pressors and  occipitomental  bandages  have  been  used  by 
surgeons  in  the  treatment  of  fVactured  jaws  since  1780. 

Drs.  F.  B.  Gunning,  of  New  York,  and  J.  B.  Bean,  of 
Atlanta,  Ga.,  were  the  first  to  describe  methods  of  construct- 
ing interdental  splints  of  vulcanite. 

When  a  dentist  is  called  upon  to  construct  an  interdental 
splint  it  will  be  in  consultation  with  a  surgeon.  He  should, 
in  justice  to  himself,  make  a  critical  examination  of  the 
case  and  determine  if  an  interdental  splint  is  indicated  or 
if  some  other  method  will  better  serve  the  patient.  If  the 
fracture  is  of  the  maxilla?  only,  and  the  teeth  are  nearly  all 
in  situ,  it  is  quite  probable  that  forcing  the  fractured  portions 
into  place  and  holding  the  lower  teeth  firmly  against  them 
with  a  cotton  padded  external  plaster  splint  and  bandage  is 
the  preferable  method  of  treatment.  Fracture  of  the 
mandible  may  be  best  treated  by  binding  the  teeth  of  the 
mandible  to  those  of  the  maxillae  with  bands  and  wires 
designed  for  orthodontia  purposes,  in  conjunction  with  an 
external  plaster  compress  and  bandage.  If  the  patient  is 
wearing  a  full  upper  and  lower  artificial  denture,  the  dentures 
may  be  securely  united  with  vulcanite,  the  upper  incisors 
removed  for  a  feeding  space,  and  used  for  the  splint.  How- 
ever, if  an  interdental  splint  is  determined  upon  it  should  be 
constructed  as  recently  described  by  Dr.  George  B.  Snow, 
of  Jiuflalo. 


432  INTERDENTAL  SPLINTS 


THE  CONSTRUCTION  OF  INTERDENTAL  SPLINTS 

Interdental  Splint. — "An  interdental  splint,  when  properly 
constructed,  forms  an  efficient  and  satisfactory  means  for 
treating  fracture  of  the  mandible,  and  the  Snow  face  bow 
and  New  Century  or  Gritman  antagonizor  are  absolutely 
necessary  for  the  attainment  of  the  correct  ahgnment  of 
their  occluding  surfaces.  For  this  reason  a  short  description 
of  the  correct  method  for  this  construction  is  appended. 

"These  instructions  apply  to  the  construction  of  the 
'Gunning'  splint.  This  separates  the  jaws  and  receives 
both  the  upper  and  lower  teeth.  It  is  retained  by  means 
of  bandages,  and  fixes  the  mandible  immovably.  It  has  a 
wide  range  of  application,  and  is  the  most  satisfactory  splint 
for  general  use.  The  Snow  face  bow  is  absolutely  necessary 
for  its  construction,  as  the  casts  must  be  placed  in  the  antag- 
onizor at  the  same  distance  from  its  joints  that  the  alveolar 
ridges  are  from  the  condyles,  or  the  bite  cannot  be  opened 
for  the  reception  of  the  splint  with  any  certainty  of  having 
correct  occlusion  when  the  fracture  has  united.  The  fact 
that  the  Snow  face  bow  has  not  been  used  is  the  common 
cause  of  failure  in  interdental  splints,  as  they  have  hereto- 
fore been  constructed. 

"  Impressions  of  the  teeth,  both  upper  and  lower,  are  first 
to  be  secured.  These  are  better  made  in  plaster,  rather  than 
modelling  compound,  for  the  plaster  is  more  easily  managed 
and  is  less  subject  to  distortion.  Very  shallow  impression 
trays  should  be  used,  the  B  mouthpiece  of  the  face  bow 
answering  the  purpose,  and  only  plaster  enough  used  to 
obtain  an  impression  of  the  teeth  to  the  gum  line.  No 
attempt  need  be  made  to  correct  any  deformity  which  may 
be  present,  and  the  operation,  if  properly  conducted,  will 
be  almost  painless  to  the  patient.  The  impression  must 
take  in  all  the  teeth  present  in  the  mouth,  for  if  the  third 
molars  are  not  included,  they  will  not  be  covered  by  the 
splint,  and  will  elongate  while  it  is  in  use,  and  so  interfere 
with  occlusion.    Fill  the  palatal  portion  of  the  upper  impres- 


THE  COXSTRUCTION  OF  INTERDENTAL  SPLINTS     433 

sion  with  sheet  wax  or  paper  just  above  the  gingival  Hne 
and  run  a  thin  cast.  Run  a  thin  horseshoe  cast  in  the  lower 
impression.  With  a  Swiss  saw  cut  this  cast  at  the  point  of 
fracture,  and  adjust  the  parts  so  that  they  make  correct 
occlusion  with  the  teeth  on  the  upper  cast.  Secure  the  two 
casts  together  with  a  very  little  sticky  wax.  Run  a  little 
plaster  on  a  piece  of  paper  and  set  the  lower  cast  into  it, 
to  hold  its  parts  in  their  correct  relation. 

"After  taking  the  impressions,  place  a  little  soft  wax  in 
the  B  mouthpiece  and  use  the  face  bow  as  heretofore  directed. 
Place  the  upper  cast  in  the  antagonizor  by  means  of  the 
face  bow,  and  it  will  be  at  the  correct  distance  from  the 
antagonizor  joints,  and  when  the  lower  cast  is  antagonized, 
their  separation  to  accommodate  the  splint  can  be  safely  made, 
and  normal  occlusion  secured  when  the  fracture  has  united. 

"Cover  the  teeth  with  No.  60  tinfoil,  letting  the  tin 
extend  beyond  the  teeth,  buccally  and  lingually,  and  cutting 
the  tin  so  that  it  can  be  put  on  without  crumpling.  Follow 
with  one  thickness  of  sheet  wax,  covering  the  teeth,  both 
upper  and  lower,  to  the  gum  line.  Separate  the  two  wax 
plates  (open  the  bite),  so  that  a  lead  pencil  will  pass  between 
them  in  front.  Connect  them  at  the  sides  with  wax,  leaving 
an  opening  in  front  extending  from  cuspid  to  cuspid. 

"A  No.  3  Snow  flask  (or  a  box  flask)  will  receive  both 
casts  and  splint.  Set  one  cast,  the  splint  being  in  place, 
the  plaster  covering  the  edge  of  the  wax,  both  buccally  and 
lingually.  Trim  and  soap  not  only  the  usual  parting  sur- 
faces of  the  invested  cast,  but  the  splint  and  palatal  surface 
of  the  other  cast  as  well.  Holding  the  loose  cast  upon  the 
splint,  run  plaster  into  the  space  between  the  two  casts,  and 
build  it  up  around  the  sides  and  rear  to  the  edge  of  the  wax. 
Trim  to  an  incline  to  the  edges  of  the  flask  all  around.  Soap. 
Place  on  ring  and  fill.  When  separating  the  flask  have  it 
warm  enough  to  soften  without  melting  the  wax.  Rap  the 
edge  of  the  flask  to  dislodge  the  centrepiece.  Remove 
and  save  the  wax,  and  find  quantity  of  rubber  required  by 
immersing  the  wax  in  a  glass  of  water.  Pack  and  vulcanize. 
The  tinfoil  being  left  upon  the  casts,  the  impression  of  the 
28 


434 


INTERDENTAL  SPLINTS 


teeth  in  the  sphnt  will  be  smooth,  and  also  larger  than  the 
teeth  themselves  by  the  thickness  of  the  foil  used.  This 
is  why  the  use  of  thick  foil  is  directed,  as  the  additional 
space  gained  by  it  renders  the  splint  more  easy  of  adjust- 
ment." 


Fig.  329 


Fig.  330 


Fig.  329  represents  both  the  wax  model  splint  and  the 
finished  vulcanite.  Fig.  330  is  a  diagram  showing  a  cross- 
section  of  the  flasked  case.  The  flask  is  designated  by  F,  the 
casts,  M;  the  plaster  encasement  by  P,  tinfoil  covering  the 


THE  CONSTRUCTION  OF   INTERDENTAL  SPLINTS     435 

teeth  with  extension  beyond  the  wax  spHnt  by  T,  and  the 
wax  model  of  sphnt  in  the  centre. 

Fig.  331  illustrates  a  splint  provided  with  arms  of  steel 
wire,  one-eighth  of  an  inch  in  diameter,  arranged  to  come 
"out  of  the  mouth  when  the  splint  is  in  position,  passing 
back  along  the  cheek  on  a  line  with  the  teeth."  This  splint 
was  invented  by  Dr.  Xorman  W.  Kingsley,  and  the  descrip- 
tion of  it  is  from  his  valuable  work  on  Oral  Deformities. 
The  splint  is  retained  in  position  by  the  submental  compress 
attached  to  the  side  bars. 

Fig.  331 


"  It  will  be  seen  that  this  splint  covers  the  lower  teeth 
only,  and  that  its  top  occludes  with  the  upper  teeth  to  admit 
of  mastication.  The  construction  of  such  a  splint  is  accom- 
plished by  placing  upper  and  lower  casts  in  an  antagonizor, 
forming  the  wax  splint  as  before  described,  arranging  the 
occlusion  so  that  the  contact  of  the  upper  teeth  will  be 
uniform,  embedding  two  stout  steel  wires  with  flattened  ends 
in  the  wax,  so  that  they  will  bear  the  strain  which  will  be 
required  of  them  while  the  splint  is  in  position.  The  par- 
ticular flask  best  adapted  for  the  vulcanizing  of  interdental 
splints  is  oblong  in  form,  and  is  larger  than  ordinary  vulcanite 
flasks;  it  is  known  as  the  box  flask." 


CHAPTER     XV 
CLEFT  PALATE  APPLIANCES 

By  cleft  palate  is  meant  a  defective  condition  of  the  roof 
of  the  mouth,  forming  an  abnormal  opening  between  the 
oral  and  nasal  cavities.  The  cleft  may  be  of  the  form  of  a 
fissure  or  of  a  rounded  hole.  The  cleft  may  be  either  con- 
genital or  acquired.  The  congenital  cleft  is  due  to  defective 
fetal  development,  but  not  accounted  for.  The  acquired 
cleft  may  be  due  to  either,  accident  or  disease.  The  extent 
of  the  cleft  may  be  from  a  slight  cleft  of  the  uvula  to  one 
extending  through  the  soft  and  hard  palates  and  the  alveolar 
process;  also  may  extend  through  the  lip  (harelip).  If  there 
is  no  harelip  complication,  the  defect  is  noticeable  only  in 
speech,  in  which  there  is  an  unmistakable  nasal  intonation. 
The  defect  is  amenable  to  both  surgical  and  mechanical 
treatment,  the  latter  of  which  only  is  considered  in  this 
chapter. 

Apparatus. — There  are  two  types  of  apparatus  for  restoring 
the  defects  of  the  roof  of  the  mouth,  known  as  obturator  and 
velum.  Of  these,  Dr.  N.  W.  Kingsley  says:  "An  obturator  is 
a  stopper,  plug,  or  cover,  hard,  non-elastic,  and  stationary, 
fitting  to  an  opening  with  a  well-defined  border  and  shutting 
of  the  passage.  Such  instruments  are  applicable  to  perfora- 
tions of  the  hard  or  soft  palate  resulting  from  accidents  or 
disease,  but  they  are  rarely  applicable  to  a  congenital  fissure 
of  the  velum.  An  artificial  velum  is  not  a  temporary  stopper, 
but  an  elastic,  movable  valve  under  the  control  of  the 
surrounding  adjacent  muscles,  closing  or  opening  the 
passage  at  will,  and  is  applicable  to  congenital  fissures, 
occasionally  where  the  soft  palate  has  been  destroyed,  but 
never  to  perforations  of  either  the  hard  or  soft  palate." 

Dr.  Kingsley  further  say's:    "In  most  cases  of  congenital 


APPARATUS 


437 


defects,  the  patient  will  acquire  correct  articulation  more 
easily  and  more  certainly  with  an  elastic  velum  scientifically 
adjusted  than  with  any  other  form  of  appliance,  because  it 
more  nearly  resembles  the  action  of  the  normal  palate  and 
will  more  readily  fulfil  its  function. 

"That  in  a  great  majority  of  cases  of  a  like  defect  a  patient 
will  never  acquire  distinct  articulation  with  an  obturator. 

"  That  where  a  pati  ent  afflicted  with  a  congenital  absence 
of  the  palate  has  overcome  the  difficulty  by  using  an  artificial 
velum  until  clear  and  distinct  articulation  has  been  acquired, 
he  may  change  the  velum  for  an  obturator,  and  continue  to 
articulate  properly. 


Tic;.    Ijijli 


"That  of  all  obturators  to  supply  deficiencies  of  the  soft 
palate  and  induce  correct  articulation,  the  one  introduced 
by  Suersen  contains  the  truest  principles  and  is  best  adapted 
to  the  purpose." 

Fig.  o32  gives  a  view  of  a  patient's  mouth,  showing  part 
of  the  cleft  palate  and  the  ajipearance  of  the  lip  after  being 
operated  upon  for  a  harelip. 


438 


CLEFT  PALATE  APPLIANCES 


Fig.  333  is  an  illustration  of  a  congenital  cleft  extending 
through  the  soft  and  hard  palate  and  also  the  alveolar  process. 


Fig.  333 


Fig.  334 


CONSTRUCTING  VELUM  AND  BASE-PLATE       439 

Fig.  334  shows  a  deft  of  the  soft  and  hard  palate,  and 
alveolar  process  depressed,  but  not  cleft. 

Fig.  335  shows  a  cleft  of  the  soft  palate  only. 

The  artificial  velum  should  rarely  extend  into  that  por- 
tion of  the  cleft  extending  through  the  alveolar  process, 
which  may  better  be  filled  with  the  hard  vulcanite. 


Fig.  335 

f^ 

PH 

■ 

r 

V 

|v 

■ 

i^^ 

J 

E 

M 

ii 

Sjmopsis  of  Technique  for  Constructing  Velum  and  Supporting 
Base-plate. — Impression  for  velum,  cast,  preparation  of  cast 
for  making  model  of  velum,  making  model  velum,  adjusting 
model  velum  to  mouth,  flasking  model  velum,  converting 
plaster  encasement  into  metal  encasement,  vulcanizing 
velum,  finishing  velum,  impression  with  the  velum  in  situ 
for  the  retaining  base-plate,  constructing  the  retaining  base- 
plate, and  attaching  the  velum. 

Impression  of  the  Cleft. — An  ordinary  impression  tray 
will  not  suffice  for  a  congenital  cleft  palate.  A  spoon  with 
the  convex  surface  of  the  bowl  upward  well  serves  for  a  tray 
to  carry  the  plaster,  or  one  of  the  two  nvsthods  described 
by  Dr.  C.  S.  Case,  of  Chicago.  He  uses  the  index  finger  with 
soft  modelling  compound  wrapped  about  it  as  the  foundation 
for  his  impression.    Having  obtained  an  imprint  of  the  cleft 


440 


CLEFT  PALATE  APPLIANCES 


in  the  compound,  it  is  chilled  and  carved  so  that  it  may  be 
held  in  the  cleft  without  contact  with  the  tissues.    It  is  then 


Fig.  336 


covered  with  a  soft  mix  of  impression  plaster,  carefully 
adjusted,  and  held  until  set;  then  removed  by  forcing  it 
backward  until  relieved  of  the  anterior  margin  of  the  cleft. 


CONSTRUCTING  VELUM  AND  BASE-PLATE      441 

Fig.  336  shows  the  completed  impression  as  taken  from  the 
mouth  for  a  cleft  of  the  soft  palate  only.    The  impression  is 


/^: 


V 


varnished  and  filled,  as  shown  in  Fij^:.  1)37.    Fig.  338  shows 
the  cast  after  removal  of  the  imj>ression.    Fig.  339  shows 


Fig.  340 


Fig.  341 


CONSTRUCTING  VELUM  AND  BASE-PLATE      443 

the  cast  carved  for  use.    Fig  340  shows  the  cleft  filled  with 
modelling  compound  carved  to  thin  edges  as  a  model  for  the 

Fig.  343 


Fig.   344 


444 


CLEFT  PALATE  APPLIANCES 


velum.    Fig.  341  shows  the  nasal  surface  of  the  same.    Fig. 
342  shows  a  side  elevation  of  the  model  velum.     Fig.  343 


Fig.  345 

■ 

iB^  . 

H 

■ 

1      -^ 

wBr  '*'"■  "      .JL. 

1 

r 

"^H^^^l 

wik 

|k,^^» 

y 

■ 

BHHHBHHI 

■K^.^-^              -        --£ 

■■■■ 

^^^^^HHI^I 

Fig.  346 


Fig.  347 


CONSTRUCTING  VELUM  AND  BASE-PLATE       445 

shows  the  finished  ^•eluIn  in  the  plaster  cast.  Fig.  344  shows 
the  skeleton  base-plate  upon  the  plaster  cast.  Fig.  345  shows 
the  wax  model  base-plate.  Fig.  346  shows  a  side  elevation 
of  the  finished  base-plate.  Fig.  347  shows  a  side  elevation 
of  combined  base-plate  and  velum.  Fig.  348  is  the  lingual 
surface  of  the  same. 

iNIost  of  the  steps  are  comprehensible  from  the  illustrations ; 
however,  there  are  several  that  are  not  and  need  elaboration. 


Velum  Model. — The  \'elum  model  is  the  first  step  after 
the  impression  that  needs  further  consideration.  Softened 
modelling  compound  is  shaped  in  the  carved  cast  by  the 
thumb  and  finger.  The  anterior  or  body  portion  of  the 
velum  is  left  thick  for  a  body,  while  the  posterior  or  curtain 
j)ortion  and  the  flanges  are  made  very  thin  with  attenuated 
edges.  I'his  is  accomplished,  so  far  as  possible,  by  molding 
the  softened  material  with  the  fingers,  after  which  it  is 
further  reduced  with  a  vulcanite  scraper  and  sandpaper. 
Jt  is  finished  with  a  cloth  wet  with  a  s(jlvent,  as  chloroform 
or  alcohol. 


446 


CLEFT  PALATE  APPLIANCES 


Adjusting  Model  Velum  to  the  Mouth.— A  hole  to  admit  a 
14-gauged  wire  is  drilled  through  the  body  of  the  velum 
model  from  the  oral  to  the  nasal  side.  A  wire  with  j  inch 
of  one  end  bent  at  right  angle  is  fitted  to  the  drill  hole  in 
model;  the  other  end  of  the  wire  is  looped  to  form  a  handle. 
This  wire  is  used  to  handle  the  model  while  adjusting  it  to 
the  cleft.  The  body  of  the  model  should  be  kept  hard,  but 
the  curtain  and  flanges  may  be  softened  as  required  by 
dipping  in  warm  water.  It  is  adjusted  by  the  patient 
swallowing,  trimming  away  excessive  material,  and  molding 
with  the  finger.  Additions  may  be  made  by  tracing  on  with 
a  pencil  of  modelling  compound.  The  velum  must  be  so 
formed  that  in  the  act  of  swallowing  it  will  entirely  close  the 
opening  between  the  oral  and  nasal  cavities.  The  desired 
form  and  adaptation  being  obtained,  it  is  chilled  and  made 
smooth.    It  is  then  ready  for  flashing. 


Fig.  349 


Flasking  the  Model  Velum. — A  small  sized  bolted  vulcanite 
flask  is  used.  The  inner  surface  of  the  flask  is  smoothed  of 
any  roughness  by  grinding,  and  smeared  with  vaseline  so 
that  the  encasing  plaster  may  be  easily  removed.  The 
model  must  be  so  encased  in  the  flask  that  the  sections 
of   the  encasement  plaster  may  be  removed,  molded,  and 


FLASHING  THE  MODEL  VELUM 


447 


reproduced  in  metal.  This  will  require  three  sections  of 
the  encasement  plaster.  Each  piece  of  the  encasement 
plaster  is  flasked  in  a  suitable  flask  (box)  with  silica  invest- 
ment compound  and  reproduced  either  in  Babbitt  or  type 
metal.  The  operation  is  simple,  but  judgment  must  be 
exercised  both  in  flasking  the  velum  model  and  the  sections 
of  the  plaster  encasement.  Fig.  349  shows  the  three  sectiosn 
of  the  Babbitt  metal  castings.  Fig.  350  shows  the  bottom 
and  middle  castings  assembled  in  one-half  of  the  flask  and 
the  third  section  in  the  other  half  of  the  flask.  P'ig.  351 
shows  the  box  flask  with  one  section  of  the  plaster  encasement 
embedded.  Fig.  352  is  the  same  with  the  plaster  model 
lifted  out,  forming  the  mold  for  casting. 


The  encasement  in  the  box  flask  must  be  heated  to  dry 
it  of  all  moisture  so  that  steam  will  not  be  formed  in  filling 
with  the  molten  metal. 

The  surfaces  of  the  castings,  which  are  to  give  form  to 
the  artificial  velum,  must  be  carefully  polished  and  burnished, 
as  they  should  produce  a  finished  surface  upon  the  velum. 

A  hole  must  be  drilled  in  both  the  upper  and  lower  sections 
of  the  castings  to  carry  a  wire  former  for  the  hole  in  the 
body  of  the  velum  to  admit  the  coupling  standard,  as  seen  in 
Fig.  350.  One  end  of  the  wire  is  cemented  into  the  casting, 
the  other  end  of  the  wire  enters  the  hole  in  the  other  section 
of  the  casting,  but  is  not  fastened. 


Fig.  351 


Fig.  352 


FL  AS  KING   THE  MODEL   VELUM  449 

The  wire  former  should  be  one  or  two  sizes  smaller  than 
the  coupler  wire. 

The  surfaces  of  the  metal  mold  must  be  soaped  and  dried 
each  time  it  is  to  be  used.  This  is  to  prevent  the  velum 
vulcanite  adhering  too  closely. 

Packing  J^elum  Rubber. — The  metal  mold  should  be  as 
warm  as  the  fingers  can  be  held  upon  without  discomfort. 
It  is  packed,  without  enmeshing  air,  with  velum  rubber 
(caoutchouc,  25;  sulphur,  5  parts),  and  vulcanized  at  300°  F. 
for  three  hours.  The  packing  should  be  carefully  done,  so 
as  to  have  as  little  excess  as  possible,  which  will  force  its 
way  out  of  the  metal  encasement. 

Finishing  the  Edges  of  the  Velum. — This  can  be  done  only 
by  trimming  with  sharp  scissors,  searing  with  a  hot  iron, 
and  rubbing  with  chloroform. 

Impression  for  the  Retaining  Base-plate. — It  is  necessary 
that  the  artificial  velum  should  be  held  accurately  in  place 
while  taking  the  impression  for  the  retaining  base-plate. 
The  surface  covered  by  the  impression  must  include  the 
thick  body  portion  of  the  velum,  the  vault  portion  upon 
which  the  supporting  base-plate  is  to  rest,  and  the  teeth  to 
which  the  base-plate  is  to  be  clasped.  The  velum  is  sup- 
ported by  means  of  a  13-gauged  soft  iron  wire.  The  end 
of  the  wire  is  engaged  in  the  coupler  hole  and  its  shaft  con- 
formed to  the  vault  and  about  the  buccal  surface  of  the 
teeth,  and  then  protrude  from  the  mouth,  the  external 
end  being  looped  for  a  handle.  The  object  is  to  so  bend 
and  shape  the  wire  that  it  will  support  the  artificial  velum, 
and  that  no  i)art  of  it,  except  the  portion  near  the  cleft, 
shall  be  engaged  in  the  impression.  The  selected  tray  is 
adjusted.  Should  the  palatal  portion  not  extend  sufficiently 
backward,  it  should  be  extended  by  an  addition  of  wax  or 
modelling  compound.  The  impression  is  then  taken  in 
I>Iaster.  The  impression  with  the  artificial  velum  in  place 
i^  varnished  and  poured  with  silica  investment  compound. 
I  jjori  tills  cast  the  clasps  are  shaped  and  the  clasp  gold 
wire  skeleton  is  formed.  The  joining  of  the  various  pieces 
of  metal  are  covered  with  wax,  and  the  rest  of  the  wire  is 
2*j 


450 


CLEFT  PALATE  APPLIANCES 


covered  with  investment  compound,  leaving  the  waxed 
joints  wide  open.  The  cast  about  the  velum  is  cut  away 
and  the  velum  removed  from  the  coupler  wire.  Investment 
is  added  to  the  exposed  end  of  coupler  wire.  The  case  is 
heated    and    soldered.     The    skeleton   frame   with   velum 


Fig.  353 


Fig.  354 


Fig.   355 


attached  is  adjusted  to  the  mouth  and  impression  taken  for 
the  vulcanite  base-plate.  The  impression  should  extend  at 
least  f  of  an  inch  back  of  the  coupler  pin.  The  impression 
will  probably  be  much  broken  in  removing  from  the  mouth; 
the  impression  and  metal  skeleton  are  assembled  without  the 


SUERSEN  OBTURATOR 


451 


velum    and    the    impression    varnished    and    poured    with 
plaster  (Fig.  344). 

If  a  gold  base-plate  is  desired,  the  first  impression  with  the 
artificial  velum  in  place  is  poured  with  plaster  (in  place  of 
investment  compound),  a  die  and  counter  formed,  the  gold 
base-plate  constructed,  and  the  coupler  pin  attached  with 
solder. 

Fig.  356 


Fia.  357 


Suersen  Obturator. — This  obturator  is  a  hard  vulcanite 
hollow  bulb  made  to  fill  the  cleft,  and  upon  which  the 
divided  palate  glides  while  speaking  and  swallowing.  The 
principal  merit  of  this  apparatus  is  that  it  is  cleanly  and 


452 


CLEFT  PALATE  APPLIANCES 


durable.    Reference  has  been  made  to  Dr.  Kingsley's  state- 
ment as  to  its  usefulness.    Figs.  353,  354,  and  355  illustrate 


Fig.  359 


three  Suersen  bulbs  (obturators),  one  of  which  is  attached 
to  a  base-plate  retainer. 


DENTURE  OBTURATOR  453 

Velum  Obturator. — The  latest  invention  for  the  reUef  of 
this  distressing  deformity  is  Dr.  Case's  velum  obturator. 
This  instrument  consists  of  a  peripheral  roll  and  an  inter- 
vening septum  of  velum  ^'ulcanite.  Figs.  350  and  357 
illustrate  this  apparatus.  A  full  detailed  description  of  the 
apparatus  is  to  be  found  in  Dr.  Case's  book. 

Denture  Obturator. — Figs.  358  and  359  show  two  views  of 
a  cast  aluminum  denture  obturator  made  necessary  from  a 
surgical  operation  for  the  removal  of  a  tumor  of  the 
maxillary  sinus. 

Referenx'E  Books. — Kingsley's  Oral  Deformities,  Ameri- 
can System  of  Dentistry,  American  Text-hook  of  Prosthetic 
Dentistry,  and  Case's  Orthopedic  Dentistry. 


CHAPTER    XVI 

ESTHETICS 

FoK  the  purpose  of  establishing  a  clear  idea  of  what  we 
mean  by  "esthetics  of  prosthesis,"  we  define  the  term 
"prosthesis"  as:  The  science,  art,  and  esthetics  of  restoring 
a  lost  dental  organ  or  organs  and  associate  parts  with  an 
artificial  substitute. 

To  understand  this  subject,  we  must  have  well-conceived 
ideas  of  the  three  terms,  science,  art,  and  esthetics.  Science 
is  classified  knowledge;  therefore,  it  is  the  involved  theory. 
Art  is  a  complex  term;  primarily,  it  means  doing  a  thing  in 
a  skilful  manner;  thus,  it  is  used  to  express  perfection  in 
any  oft-repeated  mechanical  work,  as  the  manual  labor  in 
any  of  the  useful  trades,  useful  arts  and  crafts;  and  to  the 
working  out  of  beautiful  thoughts  in  concrete  form,  fine  arts. 
As  esthetics  expresses  the  latter  idea,  we  incorporate  in 
our  definition  the  two  terms,  art  and  esthetics.  Art,  to  express 
the  skilful  doing  of  mechanical  work,  and  esthetics,  to  express 
the  harmonizing  of  our  creation  with  its  environment,  or, 
the  art  of  concealing  art.  Thus,  when  we  mean  the  skilful 
construction  of  mechanical  appliances,  we  shall  speak  of  art, 
artistic,  and  artisan;  but  when  we  mean  that  which  is  more 
than  mechanical  art,  the  ideal,  the  beautiful,  because  har- 
monious, then  we  shall  speak  of  the  esthetic  and  esthetist 
or  artist. 

Is  prosthetic  dentistry  a  trade  or  a  profession?  That 
depends  entirely  upon  how  it  is  practised.  The  science 
involved  is  not  a  factor  in  determining  whether  prosthesis 
as  practised  is  a  trade  or  a  profession;  for  both  the  useful 
and  fine  arts  may  be  highly  scientific.  If  prosthesis  is 
practised  as  a  utilitarian  art,  then  it  is,  and  can  only  be,  a 
trade:  but  if  the  utilitarian  art  is  dominated  by  esthetics, 


ESTHETICS  455 

then  and  only  then  can  it  justly  be  called  a  profession.  The 
Standard  Dictionary  defines  a  profession  as:  "An  occupation 
that  properly  involves  a  liberal  education  or  its  equivalent, 
and  mental  rather  than  manual  labor."  Hunter's  Encyclo- 
■pedic  Dictionary  defines  a  profession  as:  "A  business  which 
one  professes  to  understand  and  to  practise  for  subsistence; 
a  calling,  occupation,  or  vocation,  superior  to  a  trade  or 
handicraft."  Is  it  not  conclusive  that  a  commercial  dental 
laboratory  is  practising  "mechanical  dentistry"  only?  In 
order  to  practise  prosthesis  (Greek,  pros,  to;  tithemi,  place, 
to  place  or  restore)  it  is  necessary  that  the  patient  shall  be 
under  the  inspection  and  study  of  the  prosthetist  so  as  to 
restore  the  contour  and  harmonize  the  associated  parts. 
If  one  is  to  practise  prosthesis  as  a  profession,  he  must  be 
more  than  an  artisan;  he  must  be  an  artist.  It  is  a  common 
saying  that  artists  are  born  and  not  made.  This  saying, 
like  most  of  its  kind,  is  only  in  part  true.  However,  we  can 
say  theie  are  but  two  sources  from  which  artists  may  be 
produced,  namely,  made  and  born,  cultivation  and  intuition. 
The  idea  of  an  artist  being  cultivated  is  in  keeping  with  the 
Standard  Dictionary  definition  of  a  profession,  that  is:  "A 
liberal  education  or  its  equivalent,  and  mental  rather  than 
manual  labor."  The  artist  must  have,  in  addition  to  the 
manual  dexterity  of  the  artisan,  the  developed  mentality 
and  imagination  that  can  create  ideas  and  ideals,  and  then, 
with  his  artisan  dexterity,  he  puts  his  ideals  into  concrete 
form.  Thus,  he  makes  of  his  useful  art  a  fine  art;  and  he 
becomes  an  esthetist,  an  artist,  and  his  calling  is  a  pro- 
fession. Therefore,  if  one  would  be  an  esthetic  prosthetist, 
he  must  develop  himself  and  broaden  his  art.  The  remaining 
source  from  which  artists  are  produced,  that  is,  born,  or,  as 
we  classified  the  idea— intuition — is  an  unknown  quantity 
and  of  uncertain  value.  However,  for  a  dentist  to  depend 
upon  intuition  for  producing  esthetic  work  would  be  like  a 
preacher  depending  upon  inspiration  for  his  sermon;  too 
often  the  product  would  only  be  perspiration.  True  it  is 
that  some  people  seem  to  have  more  natural  ability  than 
others;  but  it  is  more  than  probable  that  much  of  this  seeming 


456  ESTHETICS 

inherent  or  intuitive  ability  is  the  result  of  early  cultivation 
in  ways  that  have  contributed  to  the  final  product. 

There  are  two  attributes  of  a  man  that  are  necessary  for 
success  in  any  line,  namely,  desire  and  energy.  Desire  and 
energy  is  the  celestial  fire  which  will,  when  sufficiently  strong, 
accomplish  everything.  Longfellow  has  well  expressed  the 
thought  in  this  stanza: 

"All  the  means  of  action — 
The  shapeless  masses,  the  materials — 
Lie  everywhere  about  us.     What  we  need 
Is  the  celestial  fire  to  change  the  flint 
Into  transparent  crystals,  bright  and  clear. 
That  fire  is  genius." 

Someone  has  said  that  "Genius  is  infinite  capacity  for 
painstaking."  Thus,  we  must  conclude  that  if  a  dentist 
does  not  succeed  in  reaching  high  attainments,  the  celestial 
fire  within  him  is  passive  and  not  active;  or,  that  his  energies 
have  not  been  well  directed. 

Thus  far  we  have  endeavored  to  establish  what  is  esthetics 
of  prosthesis,  and  present  the  conclusion  that  it  is  applied, 
refined  ideals  of  prosthesis,  developed  by  earnest  desire  and 
well-directed  energy. 

Dr.  Charles  Channing  Allen  has  well  expressed  the  relation 
of  esthetics  to  dentistry  in  a  paper  read  before  the  Kansas 
State  Dental  Association,  May,  1908: 

"When  a  work  is  executed  with  the  concepts  of  beauty, 
utility,  and  economy  in  their  proper  proportions,  that  work 
has  its  own  individual  characteristic,  the  evidence  of  design. 
This  is  its  passport;  its  credential;  its  hall  mark;  its  jus- 
tification. In  such  character  it  shows  whether  it  is  the 
legitimate  child  of  orderly  intelligence,  or  the  bastard  of 
bungling  incompetency.  If  it  was  fathered  by  an  under- 
standing of  the  requirements  and  a  skill  sufficient  for  their 
execution,  then  it  must  appeal  to  the  mind  as  answering  the 
requirement  of  esthetics — the  beautiful.  .  .  .  Although 
in  giving  consideration  to  design  over  mere  beauty  we  can- 
not accept  the  dictum  that  beauty  is  without  definite  utility. 
Beauty  carries  with  it  more  of  the  evidence  of  design  than 


ESTHETICS  457 

mere  utility,  for  the  esthetic  or  beautiful  appeals  to  one 
immediately,  and  does  not  require  a  systematic  proof  along 
the  recognized  lines  of  logic,  but  establishes  itself  in  the  mind 
of  the  beholder  at  once  without  proof.  Utility  alone,  as 
an  ultimate  end,  executed  without  embellishment,  may  be, 
and  usually  is,  vague  in  expressing  its  reason  for  existence, 
and  must  be  studied  and  its  purpose  analyzed,  often  labori- 
ously at  tiresome  length. 

"  No  profession  has  more  use  for  the  esthetic  and  beautiful 
than  the  profession  of  dentistry;  for  an  esthetic  restoration 
is  a  very  important  part  of  our  obligation  to  our  patient." 

We  assume  that  the  Creator  designed  that  every  soul 
should  inhabit  a  perfect  body.  According  to  its  type,  it 
should  be  like  the  Greek  creation  Apollo,  every  line  and 
every  inch  god-like  in  its  perfection.  Had  the  original 
design  prevailed,  there  could  have  been  no  beauty  associated 
with  the  human  form,  because  there  would  have  been  but 
one  type,  and  each  individual  would  have  been  a  duplicate 
of  all  others.  Beauty  is  appreciated  by  contrast  only.  The 
Creator  also  gave  the  laws  of  environment.  Therefore,  we 
have  not  two  persons  that  are  exact  duplicates  of  each 
other.  As  the  body  is  molded  and  shaped  by  external 
mental  and  physical  influences  through  conception  and 
gestation,  and  by  both  external  and  internal  mental  and 
physical  influences  through  infancy,  youth,  adult,  and 
senility,  there  can  be  no  perfect  duplicate  or  absolute  con- 
formity to  a  given  standard;  and  yet,  how  wonderfully  alike 
are  human  beings! 

Ethnologists,  physiognomists,  and  other  scientists  have 
divided  and  subdivided  the  human  family  into  many  classes 
for  the  purpose  of  better  studying  man.  So  far  as  prosthetists 
are  concerned,  our  studies  have  been  confined  almost  entirely 
to  the  Caucasian  race,  and  we  consider  only  such  classifica- 
tion as  will  aid  us  in  understanding  the  needs  of  the  pro- 
fession. We  first  divide  the  race  into  classes — light  (blond) 
and  dark  (brunette) — a  simple  classification  easily  under- 
stood, and  which  call  attention  to  certain  facts.  The  next 
classification    is   into    "temperaments,"   dividing    the   race 


458  ESTHETICS 

into  three,  four,  or  five  classes,  according  to  the  classification 
chosen.  These  divisions,  with  their  various  combinations, 
will  carry  us  much  farther  into  the  physiognomical  study  of 
our  patients;  will  establish  types,  and  teach  us  to  note  the 
variations  in  each  subject  from  the  type. 

Another  classification  we  may  call  the  "dental  profile'' 
classification.  Scientists  consider  this  subject  as  a  study 
of  the  facial  angle,  and  make  two  general  divisions — orthog- 
nathous  and  prognathous.  This  division  is  of  little  value 
to  the  dentist,  yet  the  study  of  the  profile  is  perhaps  the 
most  important  of  all  the  classifications  for  the  prosthetist. 


DENTAL  PROFILE 

For  convenience,  we  divide  the  dental  profile  into  three 
classes — straight  profile,  convex  profile,  and  concave  profile. 

Scientists  in  drawing  the  perpendicular  line  of  the  face 
have  it  touch  the  most  prominent  point  in  the  median  line 
of  the  forehead  and  the  most  advanced  portion  of  the 
maxillae.  The  dental  profile  line  is  somewhat  different  from 
the  perpendicular  facial  angle  line. 

The  first  class,  or  straight  profile,  is  the  ideal  Greek  face. 
The  perpendicular  line  has  three  points  of  contact — the 
frontal  and  mental  eminence,  and  the  middle,  of  the  wing 
of  the  nose.  The  lower  lip  will  just  touch  the  perpendicular 
line,  and  the  upper  lip  will  be  a  little  in  advance  of  the 
line.  There  is  no  question  that  this  is  the  normal  profile 
of  the  highest  ideal  of  beauty. 

The  second  class,  or  convex  profile,  has  two  points  of  con- 
tact with  the  perpendicular  line — the  frontal  eminence  and 
a  point  at  the  base  of  the  nose  which  is  the  same  distance 
from  the  middle  of  the  back  of  the  ear  as  the  frontal  eminence. 
In  the  type,  this  point  will  be  the  centre  of  the  wing  of  the 
nose. 

The  ideal  standard  of  this  class  has  the  face  made  up  of 
rounded,  graceful  curves;  forehead  high  and  slightly  receding; 
nose  of  Greek  or  Roman  type;  lips  full  but  not  coarse;  chin 


DENTAL  PROFILE  459 

receding  but  not  weak;  teeth,  both  number  and  aUgnment 
normal.  No  competent  orthodontist  would  think  of  con- 
verting this  ideal  of  our  second  class  into  the  first  or  straight 
class,  for  he  would  recognize  that  the  harmony  of  the  features 
would  be  destroyed. 

The  third  class,  or  concave  profile,  has  the  frontal  and 
mental  eminence  only  in  contact  with  the  perpendicular 
line.  It  is  not  possible  to  conceive  of  this  profile  being  a 
mark  of  beauty,  and  it  is  fortunate  that  the  class  is  small 
compared  with  the  other  two.  It  is  a  condition  confronting 
the  prosthetist,  and  he  must  place  the  features  in  as  pleasing 
a  relation  to  the  concave  line  of  the  individual  as  possible. 

The  physiognomy  of  man  is  gradually  changing  and 
tending  toward  types.  The  intermarriage  of  different 
nationalities  and  the  modes  of  living,  causing  mental  develop- 
ment and  physical  degeneracy,  partly  account  for  this 
condition.  For  the  last  few  years,  orthodontists  have  been 
impressing  upon  our  attention  the  importance  of  teeth  in 
the  physiognomy  of  man,  and  giving  us  a  rational  reason 
for  many  of  the  abnormal  conditions.  This  same  study  is 
of  value  to  the  prosthetist,  as  it  aids  him  to  understand  the 
design  of  nature  for  the  individual  case;  also  aids  him  in 
classification.  In  studying  the  harmonies  and  inharmonies 
of  the  face,  it  is  important  that  we  consider  the  causes  as 
well  as  the  effects. 

When  the  prosthetist  has  studied  the  individual  case  and 
classified  it,  he  is  confronted  with  the  question:  What  is 
one's  duty,  to  restore  the  features  to  the  natural  or  to  the 
normal  condition  ^^  It  is  apparent  that  a  normal  convex 
profile  should  not,  in  a  portion  of  its  outline,  be  converted 
into  the  concave  type,  thus  forming  an  ogee  monstrosity. 
Each  individual  case  must  be  kept  within  its  normal  class, 
then  it  is  a  matter  of  judgment  for  the  prosthetist  and  patient 
to  decide  to  what  extent  the  natural  peculiarities  shall  be 
modified. 

It  should  be  borne  in  mind  that  physiognomists  make  a 
distiMction  between  anatomy  and  expression.  Expression 
is  of  the  soul,  by  and  through  the  anatomy.     Therefore, 


460  ESTHETICS 

deformities  of  the  anatomy  may  belie  the  soul.  The  pros- 
thetist  should  study  well  to  have  the  teeth  of  the  proper 
size,  color,  form,  arrangement,  and  the  dentures  so  con- 
toured that  they  may  harmonize  with  the  rest  of  the  anatomy 
of  the  face.  The  esthetics  of  prosthesis  may  be  expressed 
thus:  Harmonious  in  anatomy  and  pleasing  in  expression. 

HARMONY 

The  preceding  chapters  of  this  book  have  been  devoted 
to  developing  the  mechanical  phases  of  prosthesis,  also 
a  reasonable  science  for  the  modes  of  procedure,  and, 
incidentally,  the  cosmetics  have  been  touched  upon.  How- 
ever, in  teaching  the  science  and  art  of  prosthesis  it  is  not 
wise  to  more  than  intimate  the  existence  of  the  esthetic, 
because  of  the  confusion  and  distraction  of  mind  created. 
The  prosthetist  must  first  become  an  artisan,  and  then, 
with  patient  endeavor,  develop  the  artist.  The  utilitarian 
art  is  the  first  consideration,  and  is  that  for  which  there  is 
the  greatest  demand;  but  for  the  mechanical  dentist  to 
dignify  his  work  and  make  himself  worthy  to  be  ranked  as  a 
professional  man,  he  must  place  the  stamp  of  ideality  upon 
the  product  of  his  hand.  As  there  are  no  two  individuals 
exactly  alike,  in  fact  no  individual,  one  side  of  whose  face  is 
the  counterpart  of  the  other,  it  is  impossible  to  establish 
fast  rules  for  esthetics.  It  is  possible,  however,  and  is  the 
province  of  this  chapter  to  map  out  certain  lines  of  thought, 
and  some  technique  as  a  means  for  harmonizing  the  work 
of  the  craftsman  with  the  environment  and  making  pleasing 
the  expression  of  the  individual.  To  recapitulate:  The 
finishing  touches  of  the  artist  shall  conceal  the  work  of  the 
artisan.  As  the  sculptor  and  painter  may  only  express  their 
thoughts  in  tangible  substance,  so  it  is  that  the  dental  esthet- 
ist  may  only  express  his  thoughts  by  means  of  the  artificial 
denture.  The  value,  therefore,  of  the  prosthetist's  creation  is 
not  in  the  intrinsic  value  of  the  physical  material  entering 
into  it,  but  in  the  quality  and  quantity  of  thought  expressed 
in  the  artificial  substitute.    The  science  and  art  of  prosthesis 


HARMONY  461 

deals  with  the  materials  and  manipulation  of  them,  whereas 
esthetics  has  to  do  with  contour  and  color  regardless  of  the 
material  used.  Contour  and  color  are  concerned  with  the 
surface  only,  therefore  the  lingual,  labial,  and  buccal  surfaces 
are  the  subjects  for  our  further  consideration  of  artificial 
dentures. 

Lingual  Surface. — The  lingual  surface  of  the  maxillse  is 
dome-shape,  but  varies  in  conformation  from  an  inverted 
V  to  a  flat  surface.  As  the  dome  of  the  mouth  is  one  of  the 
resonant  chambers,  useful  in  articulate  speech,  it  is  evident 
that  its  form  has  much  influence  in  sound  formation.  This 
does  not  imply  that  a  definite  shape  of  the  vault  is  necessary 
to  articulation,  but  it  does  imply  that  certain  confor- 
mations are  more  favorable  for  clear  enunciation  than  others, 
and  that  clear  enunciation  cannot  be  had  with  every  vault 
formation.  Therefore,  the  prosthetist  may  mar  or  improve 
the  conditions  for  good  enunciation.  The  rounded  oval 
dome  vault  is  the  best  devised  for  human  speech.  However, 
the  genius  of  mankind  is  great,  and  he  can  overcome  many 
of  the  impediments  to  soui'd  formation.  Nevertheless,  when 
he  has  acquired  the  art  of  enunciation,  any  radical  change 
in  this  resonant  chamber  will  necessitate  a  change  in  the 
manner  in  which  the  tongue  is  conformed  and  placed. 
Therefore,  it  is  logical  to  assume  that  the  conformation  of 
the  lingual  surface  of  the  artificial  denture  should  be  as  near 
the  size  and  conformation  of  the  vault  in  which  the  sub- 
ject has  acquired  good  enunciation  as  possible;  otherwise 
the  individual  will  have  to  learn  the  art  of  clear  speech  over 
again.  Chapter  I,  in  connection  with  Figs.  12,  13,  and  14, 
illustrate  the  changes  that  take  place  due  to  the  loss  of  the 
teeth.  P^ig.  12  demonstrates  that  any  unnecessary  thickness 
of  the  lingual  surface  of  the  denture  is  an  impediment  to 
speech;  however,  as  a  mechanical  appliance  is  essential  to 
restore  the  lost  tissues,  goofl  mechanics  requires  that  the 
apparatus  shall  have  a  safe  margin  of  resistance  to  the  stress 
to  which  it  may  be  siibjecte<l.  This  will  require  a  thickness 
of  material  in  the  indirect  ratio  to  the  strength,  rigidity, 
and  elasticity  of  the  material  employed.    Is  it  not  evident 


462  ESTHETICS 

that  the  carving  of  the  Ungual  contour  of  the  teeth,  gums, 
and  rugse,  as  seen  in  many  of  the  illustrations  of  this  book, 
are  more  than  fanciful,  that  it  is  the  acme  of  the  practical 
in  restoring  enunciation?  Further  than  this,  the  restoring 
of  the  rugae  is  beneficial  as  an  aid  to  the  tongue  in  deglu- 
tition. Chapter  I  should  be  read  as  a  further  elucidation 
of  this  theme.  The  technique  of  restoring  the  lingual 
surface  consists  of  the  methods  previously  described  and 
illustrated.  The  requirements  of  esthetics  are  that  the 
original  contour  of  the  lingual  surface  of  the  maxillse  shall 
be  reproduced  as  nearly  as  possible ;  that  excessive  thickness 
of  the  linguocervical  portion  should  be  employed  only  when 
other  conditions  make  them  imperative. 

Labial  Surface. — The  labial  surface  may  be  defined  as 
that  depicted  by  the  incisor  and  cuspid  teeth.  The  contour 
of  this  surface  of  the  artificial  dentures  is  to  give  support 
and  form  to  the  overlying  soft  tissues,  thus  restoring  the 
anatomical  harmony  and  aiding  in  the  expression.  There 
are  two  portions  of  this  surface  to  be  considered,  namely, 
the  gum  portion  and  the  teeth.  Chapter  I  describes  the 
change  wrought  by  resorption  of  the  alveolar  processes,  and 
the  same  chapter  explains  the  muscles  and  their  action  asso- 
ciated with  this  surface  of  an  artificial  denture. 

The  contour  of  the  gum  portion  requires  that  it  shall  not 
impinge  upon  the  frenum  labii,  nor  make  too  full  the  incisal 
fossae;  but  that  it  shall  restore  the  cuspid  eminences,  including 
the  nasobuccolabial  triangles.  As  previously  suggested,  the 
contour  for  the  individual  case  will  be  determined  by  the 
temperamental  condition.  The  contour  of  the  teeth  will  be 
influenced  by  the  temperament  and  age  of  the  patient.  In 
order  to  understand  the  temperamental  influences,  it  is 
necessary  to  digress  from  the  theme  of  study  and  consider 
abstractly  the  temperaments. 

TEMPERAMENTS 

Dr.  Jacques  defines  temperament  as:  A  state  of  the 
body  depending  upon  certain  combinations  of  the  various 


TEMPERAMENTS  463 

systems  and  organs  and  certain  functional  conditions 
affecting  them. 

The  temperaments  are  physiological  conditions  and  are 
usually  considered  unchangeable.  Dr.  Jacques,  than  whom 
there  is  probably  no  greater  authority,  states,  on  page  110 
of  his  book,  The  Temperaments,  that: 

"When  once  established,  the  temperament  inclines  natu- 
rally to  perpetuate  and  increase  itself,  since  it  gives  rise  to 
habits  that  exercise  the  organs  on  which  it  depends.  A 
change  of  temperament,  then,  implies  strong  counteracting 
influences  brought  to  bear  upon  the  constitution;  and  as 
such  strong  influences  are  in  a  majority  of  cases  lacking,  the 
inherited  tendency  is  generally  followed,  and  a  temperament 
once  established  is  maintained  thi-ough  life.  This,  however, 
is  far  from  being  universally  the  case.  The  inherent  pre- 
disposition is  sometimes  entirely  overcome  and  the  consti- 
tution radically  changed." 

There  are  various  classifications  of  the  temperaments;  but 
the  one  here  used  (because  it  is  the  one  associated  with  the 
classification  of  teeth)  is  the  one  apparently  adoptetl,  and 
described  by  Dr.  Spurzheim. 

"1.  The  Lymphatic  Temperament. — ^The  lymphatic  or 
phlegmatic  temperament  is  indicated  by  pale  white  skin, 
fair  hair,  roundness  of  form,  and  repletion  of  the  cellular 
tissue.  The  flesh  is  soft,  the  vital  actions  are  languid,  the 
pulse  is  feeble;  all  indicate  slowness  and  weakness  in  the 
vegetative,  affective,  and  intellectual  functions. 

"2.  The  Sanguine  Temperament. — The  sanguine  tempera- 
ment is  proclaimed  by  a  tolerable  consistency  of  flesh, 
moderate  plumpness  of  parts,  light  or  chestnut  hair,  blue 
eyes,  great  activity  of  the  arterial  system,  a  strong,  full, 
and  frequent  pulse,  and  an  animated  countenance.  Persons 
thus  constituted  are  easily  affected  by  external  impressions, 
and  possess  greater  energy  than  those  of  the  former  tem- 
perament. 

"3.  The  Bilious  Temperament.^ — The  bilious  temperament 
is  characterized  by  black  hair,  a  dark,  yellowish,  or  brown 
skin,  black  eyes;  moderately  full,  but  firm  muscles,  and 


464  ESTHETICS 

harshly  expressed  forms.  Those  endowed  with  this  con- 
stitution have  a  strongly  marked  and  decided  expression  of 
countenance;  they  manifest  great  general  activity  and 
functional  energy. 

"4.  The  Nervous  Temperament. — The  external  signs  of  the 
nervous  temperament  are  fine,  thin  hair,  delicate  health, 
general  emaciation,  and  smallness  of  the  muscles,  rapidity 
in  the  muscular  actions,  vivacity  in  the  sensations.  The 
nervous  system  of  individuals  so  constituted  preponderates 
extremely  and  they  exhibit  great  nervous  sensibility." 

These  four  divisions  are  spoken  of  as  primary  tempera- 
ments. It  would  be  exceedingly  difficult  to  find  an  individual 
whose  organization  complied  with  any  one  of  these  divisions 
only.  Most  persons  show  one  temperament  markedly 
strong,  but  modified  with  one  or  more  of  the  other  tempera- 
ments; while  others  possess  an  equal  blending  of  two  or 
more  temperaments.  It  is  this  blending  of  the  classes  in 
varying  degrees  that  causes  the  difference  in  the  physiog- 
nomy of  persons  and  peoples.  However,  to  study  the  com- 
plex it  is  necessary  to  reduce  it  to  its  components ;  therefore, 
the  temperaments  are  first  studied  in  the  primary  classifi- 
cation, as,  lymphatic,  sanguine,  bilious,  and  nervous;  and 
then  in  the  binary  classification,  as,  lymphatosanguine,  and 
sanguo-lymphatic,  the  one  being  the  basic  and  the  other  the 
modifying  temperament.  Unfortunately,  writers  are  not 
agreed  in  the  manner  of  forming  the  compound  noun.  Some 
writers  first  name  the  basic  and  then  the  modifier,  as,  sanguo- 
nervous;  others  reverse  the  order,  as,  nervosanguine,  both 
referring  to  the  same  physiognomical  condition.  Because 
of  this  confusion  of  nomenclature  the  writer  prefers  using 
a  phrase  in  place  of  the  compound  noun,  as,  the  sanguine 
modified  with  the  nervous  temperament,  or,  the  nervous 
modified  by  the  sanguine  temperament.  The  meaning  is 
then  unmistakable. 

Dr.  Jacques  states  that  it  is  very  difficult  to  get  portraits 
representing  the  lymphatic  temperament,  but  that  the 
illustrations  he  gives  show  its  general  tendency.  Figs.  360 
and  361  are  reproductions  of  two  of  his  examples.    The  one 


TEMPERAMENTS 


465 


to  the  left  is  modified  with  the  hiUoiis  temperament,  while 
the  one  to  the  right  is  modified  by  the  sanguine  temperament. 


Fig.  301 


Fic.  302 


:jo 


466 


ESTHETICS 


Figs.  362,  363,  and  364  are  reprodiictions  of  his  examples  of 
the  sanguine,  bilious,  and  nervous  temperaments  consecu- 
tively. 

Fig.  363 


Fig.  364 


APPLICATION 


467 


Professor  Prothero,  of  the  Northwestern  University 
Dental  School,  in  his  book  Prosthetic  Dcntistr;/,  {)resents  a 
condensed  table  of  the  primary  tem])eraments  and  their 
appropriate  teeth.  The  table  here  reproduced  will  aid  in 
fixing  in  the  mind  the  main  facts  pertaining  to  the  temper- 
aments and  their  aj^plication  to  the  selection  of  teeth  for  an 
edentulous  patient. 


Elaborate  descriptions  and  extensive  classifications  of  the 
temperaments  may  be  found  in  both  the  Anicr'mui  Sj/stnn  of 
Detitustry  and  the  American  Text-hooL-  of  Prosthetic  Dentistry. 
The  student  is  referred  to  these  works  for  a  further  in- 
vestigation of  this  subject. 


APPLICATION 

Keturiiiiig  to  the  theme,  labial  surface,  it  icinains  to  apply 
the  ideas  presented  niidcr  the  headings  Profile  and  Tempera- 


468  ESTHETICS 

ments.  This  may  best  be  done  by  use  of  a  patient.  The 
patient  (Figs.  365  and  366)  has  been  edentulous  for  many 
years.  She  is  about  sixty  years  of  age,  strongly  sanguine, 
with  a  nervous  temperament  modification.  The  sanguine 
temperament  is  indicated  by  the  generally  rounded  cast  of 
features  and  physique  of  the  blond  type.  The  nervous 
temperament  is  indicated  by  the  width  of  the  forehead  and 
by  the  toning  down  of  the  blond  type  of  coloring. 

Figs.  367  and  368  present  the  patient  wearing  artificial 
dentures  that  do  not  restore  the  harmony  of  the  face,  there- 
fore causing  her  to  appear  more  aged  than  she  is.  Notice 
the  straight  profile,  which  should  be  slightly  convex,  the 
exaggerated  lines  about  the  mouth,  the  compressed  lips,  and 
the  depressed  nasobuccolabial  triangle.  Compare  this  with 
Figs.  369  and  370,  in  which  the  features  have  been  restored 
so  that  the  lips  in  profile  are  slightly  protruding,  the  exposed 
mucous  membrane  is  natural  and  in  keeping  with  the  thick- 
ness of  the  lips.  Observe  the  gradation  from  the  thin, 
compressed,  severe,  and  repelling  expression  of  the  edentulous 
mouth,  to  that  of  the  serious,  but  cheery  and  pleasing  expres- 
sion of  the  restoration.  Surely  the  dentist's  handiwork  may 
belie  the  soul,  or  it  may  be  in  harmony  with  that  of  the 
Creator  and  Father  Time. 

Occlusion  and  Contour  Models. — Chapter  IV  instructs  how 
to  form  the  occlusion  models,  but  necessarily  the  contouring 
of  the  models  could  not,  at  that  time,  be  discussed.  Now, 
in  the  study  of  the  esthetics  of  restoration,  the  required 
contours  of  the  wax  models  should  suggest  themselves  to 
the  mind  of  the  student,  and  he  should  see  that  a  half -hour 
or  even  an  hour  spent  in  modelling  the  contour  models  is 
time  well  and  profitably  spent.  Fig.  65  shows  the  wax 
models  with  the  median  portion  and  the  incisive  fossae 
depressed,  and  the  cuspid  eminence  represented.  The  occlu- 
sal border  of  the  upper  model  overlaps  the  lower;  and  the 
lower  model  is  depressed  horizontally  to  represent  the  sulcus 
mentolabialis  of  the  external  surface  of  the  lower  lip.  While 
the  occlusion  and  contour  models  represented  in  Fig.  65 
were  not  for  this  patient,  their  conformation  is  very  similar  to 


Fio.  ■»:>') 


K-  ^ 


\jI'. 


•V'  *♦*.> 


Fin.   -.im 


Fig.  3G7 


Fig.  368 


Fig.  309 


-^£S^%ii^v>^-^V^^ 


472 


ESTHETICS 


that  which  was  required.  However,  Figs.  227,  228,  and  229 
are  of  the  denture  in  the  mouth  of  the  patient  shown  in  Figs. 
369  and  370. 

Technique  of  Model  Contouring. — The  wax  models,  having 
been  constructed  for  occlusion,  are  placed  in  the  mouth  and, 
with  the  face  in  repose,  studied  for  contour.  The  face  is 
studied  in  profile  and  in  full  front,  while  the  portion  of  the 

Fig.  371 


wax  models  to  be  added  to  or  taken  from  is  determined  by 
gentle  pressure  of  the  fingers  upon  the  external  surface  of 
the  lips.  While  conducting  this  contour  modelling  of  the 
labial  surface  of  the  wax  models,  the  prosthetist  must  be 
certain  that  the  mandible  is  in  retrusion.  The  anatomy  of 
the  parts  to  be  considered  in  the  model  restorations  are 
described  in  Chapter  I.  It  is  unnecessary  to  develop  per- 
fection of  restoration  in  the  wax  models,  for  the  final  esthetic 


APPLICATJOX 


473 


restoration  is  to  he  wroiicjlit  in  the  model  dentures,  that  is, 
with  the  porcehun  teeth  mounted  on  wax.  Little  attention 
need  be  given  at  this  time  to  the  linea  nasolabialis,  nor 
need  the  patient  be  shown  the  restoration;  indeed,  it  is  not 
well  to  call  attention  to  this  phase  of  the  construction; 
because  the  work  is  only  blocked  out  and  a  trained  imagina- 
tion is  required  to  comprehend  the  result,  which  attribute 
the  average  patient  does  not  possess. 

Fig.  372 


Buccal  Surface. — This  surface  need  not  be  considered  in 
the  (»fclu>ion  models  fi'oin  the  viewpoint  of  contour,  but 
it  needs  careful  consideration  at  the  time  of  proving  the 
occlusion  anrl  contour  f»f  the  model  dentures.     The  patient 


Pio.  374 


Fig.  375 


TEETH  475 

shown  in  Figs.  3()9  and  37(1  requires  no  buccal  restoration, 
and  this  is  true  of  probably  a  majority  of  patients. 

Fig.  371  is  a  profile  view  of  a  patient  requiring  extensive 
restoration.  Figs.  372  and  373  give  two  views  of  the  required 
artificial  dentures  as  first  developed  in  the  models  and  then 
reproduced  in  vulcanite.  Figs.  374  and  375  give  two 
views  of  the  features  restored.  The  buccal  contou 'S  do 
more  than  reduce  the  excessive  dimples  of  the  cheeks,  they 
modulate  the  linea  nasolabialis,  and  in  such  a  way  that  the 
line  is  flexible  and  graceful  both  in  repose  and  action.  If 
the  cuspid  fossae  are  built  out  in  the  artificial  denture,  for 
the  purpose  of  obliterating  these  lines  in  repose,  it  will 
produce  an  exceedingly  disagreeable  effect  when  the  mouth 
is  in  action. 

EXPRESSION  IN  ACTION 

If  the  face  were  always  in  repose  the  study  of  esthetics 
would  be  finished,  but  the  severest  test  of  the  esthetic 
creation  is  when  the  patient  is  speaking  and  laughing;  for 
then  the  size,  form,  color,  arrangement,  and  individualized 
effect  of  the  teeth  are  on  exhibition,  and  if  the  prosthetist 
has  concealed  the  art,  he  is  an  esthetist,  and  need  not  be 
ashamed  of  his  handiwork. 


TEETH 

Size. — The  size  of  the  teeth  were  considei-ed  in  the  tech- 
nique of  construction  (Chapters  I  and  VI). 

Form  and  Color. — The  form  and  color  of  the  teeth  are 
deterinined  by  the  temj)erament  when  the  j)atient  is  edentu- 
lous, but  are  selected  to  harmonize  with  the  remaining  teeth 
in  partial  cases. 

Arrangement. — The  teeth  are  arranged  as  instructed  in 
rjiaptci-  \'I,  modified  slightly  so  as  to  conform  to  the 
temperamental  indications  of  the  patient;  that  is,  the 
lymphatic  type  will  require  the  arrangement  to  be  a  trifle 


476  ESTHETICS 

flatter  and  broader  than  described  in  the  mechanical  setting 
up  of  the  teeth;  the  sanguine  type  will  require  no  change  in 
the  six  anterior  teeth,  but  the  bicuspids  should  be  slightly 
more  prominent;  the  bilious  type  will  require  the  central 
incisors  to  be  depressed  so  as  to  give  a  square  effect,  but 
no  change  distal  to  the  cuspids;  the  nervous  type  may  have 
the  centrals  more  prominent  and  the  cuspids  slightly 
depressed. 

Individualization. — Here  no  rule  can  be  established,  for 
it  is  the  little  touches,  here  and  there,  by  way  of  slightly 
rotating,  inclining,  protruding,  retruding,  extruding,  or 
intruding  one  or  more  of  the  teeth;  also  grinding,  inserting 
fillings,  and  staining  the  teeth  that  completes  the  harmony. 
This  work  should  be  done  by  the  aid  and  with  the  approval 
of  the  patient,  and  possibly  a  friend.  It  is  often  wise  to  lead 
the  patient  or  friend  so  that  they  will  suggest  the  desired 
change.  However,  this  does  not  imply  that  inartistic  and 
monstrous  desires  of  some  patients  are  to  be  complied  with, 
not  at  all,  but  if  the  patient  can  be  led  to  suggest  what  is 
really  needed,  it  will  usually  be  more  readily  accepted. 
This  will  prove  a  good  suggestion  if  properly  used.  Never- 
theless, there  are  many  patients  that  have  little  artistic 
sense,  and  cannot  be  asked  to  aid  in  this  important  task. 
Unfortunately  these  are  the  persons  who  are  later  subject 
to  the  influence  of  incompetent  critics. 

Gold  Fillings. — Gold  fillings  may  at  times  be  inserted  so  as 
to  greatly  relieve  the  artificial  effect,  especially  when  the 
patient  has  had,  for  years,  conspicuously  displayed  gold 
fillings.  In  such  cases  it  is  well  to  reduce  the  size  and  number 
of  the  fillings  and  place  them  so  as  to  give  the  appearance 
that  the  patient  has  gone  to  a  more  esthetic  practitioner. 
Gold  crowns  for  display  purposes  should  never  be  tolerated 
unless  the  patient  is  markedly  "loud"  and  nothing  less 
would  complete  the  harmony. 

Technique. — The  tooth  to  be  filled  is  cupped  out  with  a 
small  stone,  so  as  to  form  a  saucer-shaped  cavity;  dove- 
tailed grooves  may  be  cut  with  a  small  knife-edged  disk 
stone,  and  retaining  pits  made  with  a  diamond  drill  kept 


STAINING  THE   TEETH  477 

wet  with  water.  The  tooth  may  be  moiintefl  with  seahng 
wax  on  a  bk:)ck  of  wood,  as  a  means  of  support  while  filHng 
with  gold.  This  mounting  may  be  done  before  preparing 
the  cavity,  but  preferably  after  the  cavity  is  cut. 


STAINING  THE  TEETH 

The  manufacturers  of  artificial  teeth  are  to  be  commended 
for  the  excellence  of  their  product,  but  such  stock  cannot 
be  individualized  at  the  factory.  The  expert  artisans  in  the 
factory  are  most  competent  to  prepare  the  crude  earthy 
material,  grind,  comi)ress,  and  fuse  it  into  blocks  having  the 
semblance  of  teeth,  peifect  material  for  the  hand  of  the 
artist.  The  error  l^as  been  made  by  the  profession  in  that 
it  demanded  of  the  manufacturer  a  finished  product  for  the 
individual  case,  which  is  an  impossibility.  The  artist,  and 
he  is  the  dentist,  must  take  the  product  of  the  artisan  and 
individualize  it. 

The  manufacturer  has,  for  convenience  of  marketing, 
arranged  his  stock  of  teeth  'in  sets.  These  sets  vary  in 
number  from  two  to  twenty-eight  teeth,  and  are  of  uniform 
color,  that  is,  the  color,  tint  and  shade  are  the  same  in 
each  of  the  teeth;  while  in  nature  the  tint  and  shade  of  a  set 
of  teeth  vary  materially. 

Shade  and  tint  are  technical  terms  of  the  colorist.  Shade 
implies  that  a  small  amount  of  black  is  added  to  deepen  the 
color,  while  tint  is  produced  by  the  addition  of  white. 

Dr.  E.  A.  Royce,  of  Chicago,  has  called  attention  to  the 
fact  that  the  upper  central  incisors  are  the  foundation  tint 
of  the  teeth  in  a  set,  while  in  the  laterals  and  cuspids  the 
shading  is  progressive  and  then  diminishes  through  the  first 
and  second  bicuspids  and  first  molar.  The  lower  teetli 
follow  the  same  rule,  beginning  with  the  centrals  a  little 
darker  than  the  upper  centrals. 

The  amount  (jf  shading  in  each  of  the  classes  of  teeth  will 
vary  with  the  environment,  that  is,  temperament,  age, 
and  the  influences  of  waste  and  rei)air.     'J'hercfore,  for  the 


478  ESTHETICS 

manufacturers  to  attempt  to  supply,  through  the  trade, 
teeth  esthetically  constructed  for  each  individual  case  would 
result  in  a  bewildering  confusion.  The  artisans  are  doing 
well  their  part  in  supplying  stock  teeth,  but  the  prosthetist 
must  develop  the  esthetics,  otherwise  he  is  an  artisan  and 
not  an  artist.  The  operative  dentist's  claim  to  professional 
recognition  is  founded  upon  pathology;  the  prosthetist's 
professional  claim  is  based  upon  esthetics;  consequently  he 
is,  or  is  not,  an  artist. 

Materials  for  Staining  Teeth, — The  supply  houses  of  both 
this  country  and  Europe  have  placed  upon  the  market  the 
necessary  equipment  for  staining  and  changing  the  tint  and 
shade  of  teeth.  This  equipment  consists  of  a  few  colors 
(either  primary  or  mixed  colors) ,  usually  a  fluid  as  an  apply- 
ing medium,  a  mixing  spatula,  brushes,  and  a  mixing  slab  of 
glass  or  porcelain.  As  instructions  for  use  accompanying 
each  outfit,  it  is  unnecessary  to  consider  the  various  kits. 

The  colors  are  mineral  (metallic  oxides)  incorporated 
with  a  body  of  the  nature  of  glass  (sometimes  called  porce- 
lain). They  all  fuse  and  form  a  glaze  over  the  surface  upon 
which  they  are  applied.  Therefore,  to  use  them  to  change 
the  color  of  an  artificial  tooth  to  match  the  color  of  another 
as  it  comes  from  the  factory  is  not  their  intended  use. 
They  are  an  over-glaze  and  not  an  under-glaze,  that  is,  the 
color  is  on  the  surface,  not  under  the  surface.  The  various 
materials  placed  upon  the  market  vary  greatly  in  fusibility 
and  durability.  The  rule  is,  and  has  been,  invariably  true 
in  the  past  that  the  durability  is  in  the  inverse  order  to  its 
fusibility.  However,  the  last  claimant  for  consideration 
(Lenox  mineral  stains)  may  be  an  exception  to  the  rule. 
It  certainly  is  exceptional  in  some  respects.  As  the 
fusibility  of  glass  and  porcelain  products  has  been  con- 
tingent upon  the  amount  of  flux  (alkali)  incorporated,  this 
new  material  must  be  subjected  to  the  test  of  time  to  prove 
its  wearing  qualities.  The  writer  has  tested  the  Lenox 
material  wdth  the  Price  pyrometer,  and  has  found  that 
it  takes  a  very  good  glaze  with  an  exposure  of  one 
minute  at  1100°  F.,  and  that  it  resists  the  friction  of  the  felt 


STAIXIXG   THE   TEETH  479 

wheel  and  pumice  stone.  It  is  better  glazed  at  1400°  to 
1500°  F.  It  is  surprising  that  the  material  stands  2300°  of 
heat  almost  as  well  as  the  White  and  Brewster  colors,  which 
require  at  least  2000°  F.  to  give  them  a  suitable  glaze.  The 
new  product  is  ground  exceedingly  fine,  and  in  that  respect 
is  a  superior  product.  However,  until  it  has  been  demon- 
strated that  this  new  material  resists  perfectly  the  disin- 
tegrating action  of  the  fluids  of  the  mcnith,  the  writer  shall 
place  his  faith  in  the  higher  fusing  materials. 

Mixing  Fluid. — The  fluid  used  has  no  action  upon  the 
paint  material,  it  is  only  a  means  for  applying  and  retaining 
the  powdered  pigment.  Water,  gum  Arabic  water,  oils — 
as  cloves,  poppy,  lavender,  and  turpentine — also  glycerin, 
are  used.  Water  is  the  most  unsatisfactory  fluid  named. 
Of  the  oils,  that  of  cloves  is  excellent;  its  unctuous  nature 
is  its  only  drawback.  Glycerin  has  recently  been  recom- 
mended by  Dr.  Royce,  and  it  certainly  is  an  excellent 
medium. 

Technique. — The  paint  or  stain  is  spatulated  upon  the 
slab  with  the  cho.sen  medium  to  the  required  consistency 
(thick  for  deep  color,  and  thin  for  light  tint)  and  applied 
to  the  alcohol  cleansed  surface  of  the  tooth  with  a  soft 
pencil  brush.  It  may  be  more  e\enly  spread  with  a  short 
stubby  brush  used  as  a  stippler.  Certain  eft'ects  may  be 
produced  by  a  light  wiping  stroke  of  the  finger.  This  will 
remove  the  color  from  the  elevated  portions  and  leave  it  in 
the  depressions  and  grooves.  Highly  vitrified  teeth  may  be 
much  improved  by  spreading  the  color  over  the  surface 
with  a  pencil  brush  and  stippling  with  the  ball  of  the  finger. 
This  produces  the  columnar  crystalline  eft'ect  of  the  natural 
tooth.  The  painted  tooth  is  dried  in  a  moderately  warm 
plafc,  then  glazed  at  the  recpiired  temperature. 

Suggestions. — The  tooth  should  not  be  handled  with  the 
fingers  after  cleansing  with  alcohol,  but  with  clamj)ing  pliers 
attached  to  the  pins. 

The  tooth  or  teeth  while  in  the  furnace  should  be  j)laced 
with  the  face  side  ui)ward;  the  pins,  however,  should  not 
come  in  contact  with  the  bottom  of  the  furnace  or  heatiug 


480  ESTHETICS 

slab.  Place  a  quantity  of  finely  crushed  quartz  in  the  bottom 
of  the  furnace,  or  upon  the  slab,  upon  which  the  teeth  may 
rest,  and  also  as  a  protection  for  the  pins  from  too  rapid 
heating,  thus  avoiding  danger  of  checking  the  teeth. 

To  prevent  blisters  in  the  paint,  heat  up  slowly.  The  slab 
or  tray  upon  which  the  teeth  are  heated  may  be  taken  from 
the  hot  furnace  and  placed  in  a  cooling  muffle. 

Coloring. — It  should  be  remembered  that  there  are  but 
two  primary  colors  in  the  natural  teeth,  yellow  and  blue, 
but  many  tones  (degrees  of  color)  of  these  colors.  The 
color  of  the  various  teeth  is  produced  by  shading,  tinting, 
and  blending.  Therefore,  in  staining  teeth  the  primary 
color  must  be  noted  and  an  estimate  made  of  the  amount 
of  shading  a  darker  color  will  produce  before  producing  the 
characteristic  color  upon  the  surface. 

It  is  always  easier  to  deepen  the  color  of  a  tooth  than  to 
make  it  lighter. 

The  natural  teeth  are  constantly  growing  darker  with  age, 
just  in  the  ratio  to  the  change  in  the  natural  complexion  of 
the  patient.  This  is  due  to  the  fact  that  the  teeth  belong 
to  the  dermal  tissue  and  both  are  pigmented  by  the  cir- 
culating fluids  of  the  body.  Therefore,  in  coloring  or  stain- 
ing the  teeth  they  may  be  shaded  a  little  darker  than  the 
natural  ones  and  be  less  conspicuous. 

The  natural  teeth  are  subject  to  many  external  coloring 
influences,  as  smoking  and  chewing  tobacco  or  other  drugs, 
discolored  incipient  decay  or  white  or  yellow  spots  from 
defective  calcification  of  the  teeth. 


APPLIED  ESTHETICS 

A  few  practical  cases  will  suffice  to  elaborate  this  phase 
of  the  subject. 

Figs.  376  and  377  is  the  patient  previously  presented, 
laughing.  Fig.  376  shows  the  gum  of  the  gum  section  teeth, 
although  much  retruded.  The  teeth  are  undersize  and  have 
the  artificial  appearance   of   their   type.     Fig.   377  shows 


Fig.  376 


Fig.  37 


;n 


482 


ESTHETICS 


another  view  of  the  contour  as  illustrated  in  Figs.  369  and 
370  properly   restored,    and   if   the   teeth   are   of   suitable 


Fig.  37S 


Fig.  379 


form,  size,  color,  and  individualized,  they  appear  like  well- 
j:rcservcd  natural  teeth.     If  they  do  not  harmonize  in  every 


APPLIED  ESTHETICS 

Fig.  3S1 


483 


Fig.  382 


Vu:.  -.is:'. 


Fk;.   :iS4 


Fig.  385 


Fig.  386 


APPLIED  ESTHETICS 


485 


respect  the  artificiality  of  the  dentures  is  more  conspicuous 
than  in  the  old  ones. 

Figs.  378  and  379  present  two  views  of  a  patient;  the  one 
upon  the  left  shows  the  upper  of  a  gum  section  set  that  had 


Fig.  387 


been  worn  for  thirty  years.  The  gum  portion  shows  also 
the  undersized  youthful  appearance  of  the  teeth.  The  lower 
teeth  are  entirely  out  of  sight.  The  mouth  is  much  better 
restored  in  the  view  upon  the  right.    While  the  dentures  in 


486 


ESTHETICS 


Fig.  389 


Fig.  390 


APPLIED  ESTHETICS 


487 


Fiu.  3lt2 


^J 


ESTHETICS 


Figs.  380  and  381  are  not  the  ones  in  the  patient's  mouth, 
they  are  almost  duphcate. 

Figs.  382  to  387  show  the  patient  and  teeth  constructed 
to  the  mouth  of  the  Wilhams  truebite  teeth.  The  teeth 
were  all  stained  except  the  upper  second  molars,  which 
were  left  unstained  to  show  the  change  produced  by  staining. 
The  effects  can  be  seen  in  the  photos,  but  it  is  doubtful  if 
it  will  be  apparent  in  the  half-tones. 

Fig.  394 


Fig.  395 


Figs.  388  to  391  show  different  phases  of  esthetic  restor- 
ation in  continuous  gum  work.  This  is  the  completed 
case  the  skeleton  of  which  is  shown  in  Figs.  323  and  324, 

Figs.  392,  393,  and  394  are  views  of  a  continuous  gum 
upper  and  cast  metal  lower  that  has  been  doing  service  for 


APPLIED  ESTHETICS 


489 


some  years.    The  dentures  had  been  worn  four  years  when 
the  photos  were  taken. 


Fig.  396 


Figs.  395  and  39G  are  two  views  of  a  case,  requiring  a 
unilateral  restoration,  of  a  crescent-shaped  face  viewed  from 
the  front. 


INDEX 


A 


Adhesion  bv  oontact  in  rotpiition, 

274,  284 
Alabaster,  59 

Alcohol  heat  for  vulcanite,  231 
Alkalies  for  dental  porcelain,  313 
Alloys  of  gold,  364 
Aluminum,  339 
base-plate,  340 

Billmeyer  castinji  bucket   for, 

346 
burnishing  of,  356 
carbon  compounds  and,  349 
casting  of,  340,  350 

Billmeyer  metho<l  for,  341 
cooling  of,  351 
to  porcelain  teeth,  35(5 
removal  of,  351 
crucible  model  for,  349 
P^lgin     vacuum     casting    ma- 
chine and,  358 
flaskingof,  353,  34(i 
imjjression  for,  341 
inelasticity  of,  353 
inv(!stment-comj)Ound   cast 

for,  341 
metal  for,  349 

melting  of,  350 
occlusion  of  gases  and,  349 
oxidation  and,  350 
polishing  of,  354 

f)reparations  for,  354 
relief  chamber  for,  342 
sprue  formers  for,  344 
swaged,  358 

attachment  of,  to  vulcanite, 
36U 
use  of,  353 
vacuum  chamber  for,  342 


Aluminum  base-plate,  wax   model 
base-plate  for,  342 
chemical  properties  of,  339 
history  of,  339 
physical  properties  of,  339 
swaging  of,  by  die  and  counter- 
die  method,  359 
by  Lyon  swager,  363 
by  machine  methods,  361 
by  Olivian  swager,  363 
by  Parker  shot  swager,  363 
Alveolar  processes,  38 

closure  of  .soft  tissues  over,  51 
development  of,  38 
examination  of,  50 
influence  of,  oti  form  of  base- 
plate, 50 
resorption  of,  38,  39 

appearance  after,  51,  52 
time  of,  50 
"Anatomical    articulation,"   Bon- 
will's,  36 
Anchorage  for  porcelain  t(;eth,  321 
Annealing  in  swaging  of  gold  base- 
plate, 376 
Antagonization,    mechanico-ana- 
tomical,  in  vulcanite  dentures, 
241 
of  model  dentures,   i)roving  of, 

247 
in  vulcanite  dentures,  241 
Antagonizor,  Kit) 
Honwill's,  166,  168 
Christensen's,  169 
distinction  of,  from    ;irt  iciihitor, 

165 
lOvans',  166,  167 
(Jritinan's,  lt)9 
Clysi's,  171 

mounting  of  casts  upon,   179 


492 


INDEX 


Antagonizor,  Hayes',  167 
history  of,  166 

mounting  on,  in  vulcanite  den- 
tures, 236 
removal  of  model  dentures  from, 

249 
Snow's,  170 

mounting  of  casts  upon,  177 
use  of,  176 
Walker's,  168,  169 
Arch,  dental,  47 

Articulation,    "anatomical,"   Bon- 
will's,  36 
temporomandibular,  23 
Articulator,  165.     See  also  Antag- 
onizor. 
anatomical,  165 
definition  of,  165 
distinction  of,  from  antagoni/or, 

165 
Kerr's,  141 
Artificial  dentures,  casts  for,  1 13 

retention  of,  272 
Asbestos  block  for  soldering  con- 
tinuous gum  dentures, 
421 
of  gold,  383 
Atmospheric    pressure    plate,   274 

in  retention,  287 
"Automaton"  blowpipe,  385 


B 


Babbitt  metal,  composition  of,  373 

for  die,  373 
Bailey  flask,  366 

Baking   of   continuous   gum   den- 
tures, 428,  429 
Balancing  curve,  short,  in  vulcan- 
ite dentures,  242 
Bar,   lower,  clasp  attachment  for, 
405 
cope  for,  410 
correction  of  too  close  fit  in, 

405 
crib  attachment  for,  407,  408 
dentures,  401 

double  wire  method  of,  405 
materials  for,  402 
single  wire  method  of,  402 
tang  attachment  for,  410 
technique  of,  402 


Base    metal    pins    for    porcelain 

teeth,  327 
Base-plate,  aluminum,  340 

cheoplastic,  413 

construction  of,  126 

for  double  vulcanization,  329 

form    of,    influence    of    alveolar 
processes  on,  50 

gold,  364 

gutta-percha,  131 

materials  for,  126 

metal,  133 

modelling  compound,  128,  130 

for  occlusion  model,  126 

outline  of,  122 
in  retention,  283 

paraffin,  127 

platinum,    for    continuous    gum 
denture,  420 

resinoid  preparations  for,  131 

retaining,    for    artificial    velum, 
449 

tin,  126,  413 

vulcanite,  131,  234 

wax  model,  for  aluminum,  340 
Basle   Anatomical   Nomenclature, 

32 
Bean's  alloy,  413 
Beeswax,  56 

adulteration  of,  57 

composition  of,  57 

manipulation  of,  57 

melting  point  of,  57 

solvents  of,  57 

white,  56 

yellow,  56 
Bicuspids    in    vulcanite    dentures, 

intercuspation  of,  240 
Bilateral  vacuum  chambers,  291 
Bilious  temperament,  463 
Billmeyer  casting  bucket  for  alumi- 
num base-plate,  346 

method  for  casting  of  aluminum 
base-plate,  340 
Bismuth  compound  for  die,  373 
Bite,  124 

dental,  definition  of,  124 

gauges  in  occlusion  models,  137 
Snow's,  137 

hunk-,  124 

mush-,  124 

quash-,  124,  125 

technique  of,  125,  126 


INDEX 


49;: 


rigid    cla.sps, 
ill     artificial 


Bite,  use  of,  125 

wax-,  124 
Block  formation,  cubical,  |)laue  of 
teeth  and,  21,  21 

porcelain  teeth,  325 
Blow-ofT  for  vulcanizcr,  207 
Blowpipe,  3S4 

"automaton,"  385 

flame,  387 

mechanical,  385 

use  of,  386 
BXA  classification  of  teetli,  32 
Body  for  porcelain  teeth,  315 
Bonwill's     "anatomical     articula- 
tion," 36 

antagonizor,  166,  168 

demonstration    of    parabolic 
curve,  34 
Box  vulcanite  flask,  202 
Brushes,  226 

for  polishing,  226 
Bryant    method   of 

303 
Buccal     restoration 

dentures,  473 
Buckling  in  swaging  of  gold  base^ 

plate,  378 
Buffers,  224 

construction  of,  226 

for  polishing,  224 
Buffing,  228 

method  of,  228 

of  vulcanite,  228 
Bunsen  burner,  230 

construction  of,  231 
flame  of,  231 
Burner,  Bunsen,  230 

jeweller's  triple,  230 
Burning  of  porcelain  teeth,  318 
Burnishing     of     aluminum     base 

plate,  350 


Calci.n'kd  i)laster,  60 

Caoutchouc,  183 
chemistry  of,  185 
composition  of,  185,  1S6 
history  of,  183 
imjiurities  in,  185 
[ircparaMoii  of  crude,  1K4 
properties  of,  physical,  IS4 


Caoutchouc,  purification  of,  185 

solvents  of,  185 
Carborundum,  223 
composition  of,  223 
manufacture  of,  223 
for  polishing,  223 
wheels,  224 
Case's   method   of   impression   for 

artificial  velum,  4S<) 
Casting  for  aluminum  base-plate, 
340,  350 
for  gold  base-plate,  365 
for  tin  base-plate,  413 
for  vacuum  chambers,  290 
Casts,  109 

for  artificial  dentures,  113 

velum,  441 
definition  of,  109 
distinction  of,  from  model,  109 
for  double  vulcanization,  328 
French's  dental  plaster  for,  111 
for  gold  base-plate,  366 
investment  compounds  for,  112 
luting  of  model  dentures  to,  249 
materials  for.  111 
mounting  of,  176 

upon  antagonizor,  Gysi's,  179 

Snow's,  177 
with  face  bow,  178 
upon  occlusion  frames,  177 
partial,  120 

oxyphosphate  of  zinc  cement 

for,  121 
pouring  of,  120 
repair  of,  121 
plaster  of  Paris  for,  111 
Price's  artificial  stone  for,  112 
removal  of,  from  plaster  impres- 
sions, 119 
separation  of,  from  impression, 

118 
Spence's  plaster  compound  for, 

111 
uses  of,  110 

for  vulcanite  dentiu'es,  234 
silex  method  in,  253 
tin  method  in,  253 
wax  and  com}K)unds  for,  113 
removal  of,   in   vulcanite  den- 
tures, 2()2 
Celluloid    models,    j)orcelain    teeth 

for,  323 
Cement  phister,  60 


494 


INDEX 


Chalk,  prepared,  for  polishing,  228 
Charcoal    block    for    soldering    of 

gold,  383 
Cheoplastic  base-plate,  413 
Chisels,  vulcanite,  218 
Christensen's  antagonizor,  169 
Chucks  for  lathes,  220 
Clamp,  C,  for  swaging  of  gold  base- 
plate, 377 
Clasp    attachment  for  lower  bar, 
405 
gold,  365 
Clasps,  296 

adaptation  of,  to  teeth,  306 
advantages  of,  296 
attachment  of,  location  of,  308 

to  plate,  308 
balancing  of  plate  by,  304 
disadvantages  of,  296 
formation  of,  with  pliers,  307 
location  of,  304 
names  for,  296 
phers  for,  307 
retention  by,  296,  304 
rigid,  297,  302 

Bryant  method  of,  303 
Schwartz  method  of,  303 
soldering  of,  to  partial  gold  base- 
plates, 399 
spring,  297,  298 
fiat,  302 
forms  of,  301 
half-round,  302 
materials  for,  301 
round, 301 

teeth  for,  choice  of,  299 
form  of,  299 
longitudinal       portion      of, 

clasped,  300 
portion  of  circumference  of, 
clasped,  300 
use  of,  298 
stay,  297 

use  of,  297 
teeth  for,  gripping  of,  305 
Cleft  palate,  436 

appliances  for,  436 
harelip  and,  436 
obturator  for,  436,  451 
denture,  453 
Suersen,  451 
velum,  453 
velum  for,  436 


Close's  continuous  gum  material, 

417 
Cohesion  surface  forms,  Speyer's, 

for  retention,  294 
Coloring  of  teeth,  480 
Compensating  curve,  22 

in  vulcanite  dentures,  242 
Complete  vulcanite  dentures,  233 
Compressibility  of  plaster,  62,  63 
Concave  profile,  459 
Condyle  of  mandible,  23,  24 
paths,  angles  of,  152 
table  of,  152 
average  forms  of,  153 
determination  of,  137 

Gysi's  instruments  for,  142 
in  occlusion  models,  137 
Snow  bite  gauges  for,  137 
Walker-Christensen-Snow 
method  of,  141 
Cone,  truncated,  view  of  teeth  as, 

36 
Contact,  three  point,  compensating 

curve  and,  22 
Continuous  gum  body,  417 
dentures,  416 

asbestos  soldering  block  for, 

421 
baking  of,  428,  429 
body  for,  application  of,  426 

second,  428 
enamelling  of,  429 
equipment  for,  417 
furnaces  for,  418 
Custer's,  418 
gasoline,  419 
Price's  418 
pyrometer  for,  418 
investment  for,  422 
iridoplatinum  wire  for,  420 
magnesia     soldering     block 

for,  421 
materials  for,  416,  417 
platinum  and,  416 

base-plate  for,  420 
polishing  of,  429 
porcelain  for,  417 

application  of,  426 
reenforcing  wires  for,  423 
repair  of,  430 
shrinkage  in,  427 
solder  for,  421 
technique  of,  420 


INDEX 


495 


Continuous    gum    dentures,   teeth 
for,  421 
soldering  of,  421 
material.  Close's,  417 
Contour    models,    123.      See    also 
Occlusion  models, 
proving  of,  for  doiible  vulcani- 
zation, 330 
Contraction  of  plaster,  62 
Convex  profile,  45S 
Cope   attachment    for    lower  bar, 

410 
Cores  for  gold  base-plate,  36S 
Corundum,  223 

comf)osition  of,  223 
manufacture  of,  223 
for  i)oIishing,  223 
Counter-die,  construction  of,  375 

for  gold  base-plate,  374 
Countersunk     pin     for    porcelain 

teeth,  324 
Crib    attachment   for   lower   bar, 

407,  408 
Cross-bar  vulcanizer,   I.ewis,  20G 
Crucible  mold  for  aluminum  base- 
plate, 349 
Cubical  block  formation,  plane  of 

teeth  and,  20,  21 
Curve,  compensating,  22 

distinction  of,   from   curve  of 

Spec,  22 
three-poii'.t  contact  and,  22 
parabolic,  34 

iionw  ill's  demonstration  of,  34 
determination  of,  34,  3.5 
modifications  of,  34 
of  Spec,  21 

curvature  of,  22 
distinction  of,   from   coiii]K'n- 
sating  curve,  22 
Custer's  furnace,  418 


"  Dkau-isuknku"  gypsum,  61 
Oeglutition  test  for  model  dei;tnre, 

247 
Dental   arch,  distinction    of,   frf)iii 
denial  vault,  47 
oxarnination  of,  47 
shape  of,  47 
porcelain,  311 


Dental  profile,  438 

vault,  examination  of,  47 
Dentistry,  relation  of,  to  esthetics, 

456 
Denture  obturator,  453 
Dentures,  artificial,  buccal  restor- 
ation in,  473 
ca.sts  for,  113 
full,  retention  of,  277 
labial  surface  of,  462 
lingual  surface  of,  461 
retention  of,  272 
soft  palate  and,  30 
'sticking  up"  of,  281 
vulcanite  in,  197 
bar,  lower,  401 
continuous  gum,  416 
model,    for    vulcanite   dentures, 

246 
partial    lower,    gold    base-plates 
for,  401 
upper,    gold    base-plates    for, 
396 
vulcanite,  complete,  233 
Detachable  tray  method  in  partial 

upper  impre.ssions,  102 
"Diatoric"  porcelain  teeth,  322 
Die,  372 

Babbitt  metal  for,  373 
bismuth  compound  for,  373 
and    counter    method    for    gold 

base-plate,  365 
metal  for,  372 
pouring  of,  374 
zinc  for,  372 
Disks  for  retention,  291 
Donham's  vulcanite  flask,  202 
Double  vulcanization,  328 
Doublers,  381 
formation  of,  381 
for  partial  gold  base-plate,  381 
s<jldering  of,  to  gold  base-plate, 
388 


£ 


1';i-io(;ti{1(;  lathes,  219 
J'^lgin     vacuum     casting    macliiru 
358 


J']! 


nery. 


for  polishing,  223 
Kminenlia  articularis,  23 


49G 


INDEX 


Enamelling    of    continuous    gum 

dentures,  429 
Enamels  for  porcelain  teeth,  315 
Encasement,  metal,    for    artificial 

velum,  447 
English  double  punch,  394 
Enlarged  raphe,  impressions  for,  94 
Equalized  pressure  test  for  model 

dentures,  247 
Eruption  of  teeth,  37 
Esthetics,  454 

applied,  480 

relation  of,  to  dentistry,  456 
of  occlusion  models  to,  46S 

teeth  and,  475 
Evans'  antagonizor,  166,  167 
Expansion  of  plaster,  62 
Expression,  facial,  in  action,  475 

muscles  of,  28 


F 


Face,  anatomy  of,  17 

bow,  mounting  of  casts  with,  178 
occlusion  models  and,  138 
Snow's,  138 

interdental  splints  and,  432 
technique  of,  139 
use  of,  138 
divisions  of,  17 
ideal  Greek,  18 
Facial  expression  in  action,  475 
Feldspar,  311 

composition  of,  311 
for  dental  porcelain,  312 
preparation  of,  312 
Ferrules,  287,  303 

for  gold  base-plate,  410 
indications  for,  303 
Files  for  vulcanite,  217 
Finishers,    soldering    of,    to    gold 
base-plate,  388 
wire,  soldering  of,  to  gold  base- 
plate, 390 
Finishing  of  artificial  velum,  449 

of  partial  vulcanite  dentures,  265 
Flame  method  for  removal  of  teeth 

from  vulcanite  dentures,  266 
Flask,  closing  of,  cloth  for,  256 
dangers  in,  256 
for  double  vulcanization,  333 
for  gold  base-plate,  366 


Flask,  heating  of,  252 
opening  of,  251 
placing  of,  in  vulcanizer,  257 
press,  202 

Buffalo  Dental    Manufactur- 
ing Go's.,  No.  2,  206 
power  of,  206 
removal    of     vulcanite    denture 
from,  258 
from  vulcanizer,  258 
of  wax  from,  251 
Snow,  for  interdental  splints,  432 
vulcanite,  200 
box,  202 
Donham's,  202 
Whitney's,  202 
Wilson's,  202 
Flasking  of  aluminum  base-plate, 
346,  353 
for  double  vulcanization,  333 
of  model  for  artificial  velum,  446 

dentures,  249 
of  partial  vulcanite  dentures,  263 
Flask-tongs,  217 
Flat  spring  clasps,  302 
Flooring  plaster,  60 
Flux  for  porcelain  teeth,  315 

for  soldering  of  gold,  384 
Fossa,  glenoid,  23 
Frame,  occlusion,  165 
French's  dental  plaster  for  casts, 

111 
Frits  for  porcelain  teeth,  315 
Full  artificial  dentures,   retention 
of,  277 
lower  gold  base-plate,   swaging 
of,  379 
impressions,  90 
Furnaces  for  continuous  gum  den- 
tures, 418 
Fusible  metal  method  for  repair  of 
vulcanite  dentures,  269 


G 


Gas  stove  heat  for  vulcanite,  231 

Gasoline  furnace,  419 
heat  for  vulcanite,  231 

Gas-regulator  for  vulcanizer,  207 

Glandular  tissues  of  mouth,  exam- 
ination of,  52,  53  '' 

Glenoid  fossa,  23 


INDEX 


497 


Glossing,  229 
method  of,  229 
of  vulcanite,  229 
Glycerin   method   for   removal   of 
teeth   from   vulcanite   dentures, 
266 
Gold,  alloys  of.  364 
base-plate,  ."36-1 

attachment     of,     to     natural 

teeth,  409 
cast  for,  366 
cores  for,  368 
counter-die  for,  374 
die  for,  372 

and  counter  method  for,  365 
edge  of,  turning  of,  389 
ferrules  for,  410 
flask  for,  366 
Bailey,  366 
Hawes'  parting,  370 
Lewis,  366 
full  lower,  swaging  of.  379 
impression  for,  366 
methods  for,  365 
casting,  365 
swaging,  365 
model  for,  366 
molding  for,  366,  370 
sand  for,  370 
technique  of,  371 
partial,  396 

casting  method  for,  400 
doublers  for,  381 
lower  dentures,  401 
soldering  of  clasps  to,  39!^ 
Spence    plaster    compound 

for,  399 
swaging  of,  380,  398 
files  for,  380 
nriodels  for,  379,  380      * 
nippers  for,  380 
for  partial  upper  dentures,  396 
repair  of,  411 

.soldering  of  attachments   to, 
388 
of  buccal   finishers   to,  389 
of  doublers  to,  388 
of  finishers  to,  388 
of  labial  finishers  to,  3K9 
of  porcelain  to,  394 
backing.s  for,  394 
investment  for,  395 
cooling  of,  396 
32 


Gold  base-plate,  soldering  of  porce- 
lain   to,   investment   for, 
heating  of,  396 
of  retainers  to,  391 
of  teeth  in,  392 
warping  in,  392 
of  wire  finisliers  to,  390 
swaging  of,  365,  375 
annealing  in,  376 
buccal  finishers  to,  389 
buckling  in,  378 
C  clamp  for,  377 
half  counter-die  for,  377 
horn  mallet  for,  377 
labial  finishers  to,  389 
pattern  for,  375 
"jjickle"  for,  377 
rubber  mallet  for,  777 
characteristics  of,  364 
cla.sp,  365 

finings,  teeth  and,  476 
fineness  of,  standard  of,  364 
plate,  364 
solder,  364 
soldering  of,  382 

asbestos  block  for,  383 
blowpipe  for,  384 
charcoal  block  for,  383 
flux  for,  384 
holders  for,  383 
investment  compound  for,  382 
magnesia  block  for,  384 
technique  of,  382 
swaging  of,  365 
Greene's    method    for    full    upper 

impre.ssions,  87,  88 
Grinding  of  vulcanite,  218 
Gritman's  antagonizor,  169 
Gum  dentures,  continuous,  416 
enamel,  417 
flabby,  in  full  upper  impressions, 

80 
porcelain  teeth,  319,  325 
"section"  porcelain  teeth,  325 
Gunning  interdental  splints,  432 
Gutta-percha.  58 
ba.se-plate,  131 
.source  of,  58 
u.se  of,  .59 
Gypsum,  .59 

burning,  chemistry  of,  60 
composition  of,  chemic.il,  .59 
"dead-burn(;d,"  61 


498 


INDEX 


Gypsum,  impurities  in,  59 
massive,  59 

products,  grinding  of,  61 
rock,  59 
Gysi's  antagonizor,  171 

mounting  of  casts  upon,  179 
measuring  instruments,  142 

determination     of     condyle 

path  with,  143 
large  register,  143 
location   of   condyles   with, 

144 
small  register,  152 
technique  for,  143,  144 


H 


Half-round  spring  clasps,  302 

Hands,  cleansing  of,  for  examina- 
tion of  mouth,  44 

Hard-finish  plaster,  60 

Harelip,  cleft  palate  and,  436 

Harmony,  460 

Hawes'  parting  flask,  370 

Hayes'  antagonizor,  167 

Heat  for  vulcanite,  229 

Horn  mallet  for  swaging,  377 

Hunk-bite,  124 

Hydrogen  sulphide  in  vulcanite, 
194 

Hydrostatic  law  of  retention,  273 


Impression,  55 

for  aluminum  base-plate,  341 

for  artificial  velum,  439 

definition  of,  55 

for  double  vulcanization,  328 

for  enlarged  raphe,  94,  95 

filling  of,  116 

full  lower,  90 

classification  of,  90 
ridge  in,  broad,  90,  92 
flat,  93 
high,  90 
thin,  93 
technique  of,  90 
upper,  classification  of,  69 
flabby  gum  in,  83 
flat  \^ults  in,  SO,  81 


Impression,    full    upper,    Greene's 
method  for,  87,  88 
high  vaults  in,  79 
interspersed  hard  and  soft 

tissues  in,  83 
modelling     compound     for, 

86,  87,  88 
"muscle  trimming"  in,  87 
normal,  69 

plaster  for,  mixing  of,  73 
position  of  patient  in,  73 
reenforcement  for,  83 
removal  of,  76 
soft  tissues  in,  80 
technique  of,  69 
traj^  in,  adjustment  of,  70 
filling  of,  75 
insertion  of,  75 
placing  of,  75 
reenforcing  of,  71 
for  gold  base-plate,  366 
gutta-percha  for,  58 
for  interdental  splints,  432 
for    lower   vulcanite     dentures, 

261 
materials  for,  56 
modelling  compound  for,  58 
partial  lower,  104 

classification  of,  104 
upper,  95 

alternating  teeth  and  spaces 

in,  98 
anterior  teeth    in,    loss   of, 

95 
classification  of,  95 
detachable  tray  method  in, 

102 
isolated    teeth    method    in, 

101 
posterior  teeth  in,  loss  of,  98 
plaster  of  Paris  for,  59 

removal  of,  from  casts,  119 
pouring  of,  116 
preparation  of,  113 
for  retaining  base-plate  for  arti- 
ficial velum,  449 
scheme  for,  55 
sejaarating  fluids  for,  114 
separation  of,  from  casts,  118 
trays,  63 
body  of,  63 
definition  of,  63 
distinction  of,  from  cups,  63 


INDEX 


499 


Impression  trays,  flanges  of,  63 
floor  of,  63 
forms  of,  64 
handle  of,  63,  64 
materials  for,  63 
nomenclature  of,  63 
removal  of,  in  vulcanite  den- 
tures, 261 
surfaces  of,  64 
for   upper    vulcanite    dentures, 

261 
use  of,  113 
varnishes  for,  115 
for  vulcanite  dentures,  234 
wax  for,  56,  57 
Incisor  path,  registration  of,  156 
India-rubber,  183.     See  Caout- 
chouc. 
Inferior  maxilla,  250.     See  Man- 
dible. 
Interdental  .splints,  431 
cast  for,  433 
construction  of,  432 
Gunning,  432 
impressions  for,  432 
Snow  face  bow  and,  432 
flask  for,  432 
Iridoplatinum  wire  for  continuous 

gum  dentures,  420 
Ironing-in    method    for    repair    of 

vulcanite  dentures,  271 
I.solatcd   teeth  method   in   partial 
upper  impressions,  101 


Jaw,  development  of,  eruption  of 
teeth  and,  38 
lower,  25.     See  Mandible. 
Jeweller's  triple  burner,  230 


K.\oLix,  313 

composition  of,  313 

for  dental  porcelain,  313 

use  of,  313 

Kerr  "articulator,"  141 

Kingsley's  alloy,  413 

Knives,  plaster,  122 


Labial  surfaces  of  artificial  den- 
tures, 462 
Lathes,  218 

care  of,  221 

chucks  for,  220 

electric,  219 

polishing,  218 

power  for,  218 
Le  Chatelier's  theory  of  setting  of 

plaster,  61 
Lenox  mineral  for  staining  of  teeth, 

477 
Leverage  in  retention,  275,  284 
Lewis  cross-bar  vulcanizer,  206 

flask,  366 
Line,  naso-auditory-meatus,  19 
Lines  in  occlusion  models,  marking 

of,  136 
Lingual  surfaces  of  artificial  den- 
tures, 461 
Lower  impressions,  full,  90 
partial,  104 

jaw,  25.    See  Mandible. 
Luting  of  model  dentures  to  casts, 

249^ 
Lymphatic  temperament,  463 
Lyon  swager,  363 

M 

Magnesia     block     for     soldering 
continuous      gum      den- 
tures, 421 
of  gold,  384 
Mallet,  horn,  for  swaging,  377 

rubber,  for  swaging,  377 
Mandible,  25 

body  of,  25 

condyle  of,  23,  24 

relation  of,  to  glenoid  fo.ssa,  24 

importance  of,  25 

mastication  and,  26 

movements  of,  25 

muscles  of,  26 

rami  of,  25 
Mandibular  surfaces,  size  of,  sig- 
nificance of,  49 
.Maiiifolder  for  vulcanizer,  207 
Massive  gypsum,  59 
Ma.stication,  41 


500 


INDEX 


Mastication,  loss  of  teeth  and,  43 
mandible  in,  26 
muscles  of,  26 
purpose  of,  41 
Maxilla,  inferior,  25.  See  Mandible. 
Maxillary  raphe,   examination  of, 
48 
surfaces,  size  of,  significance  of, 

49  1 

suture,  examination  of,  48 
Measuring  instruments,  Gysi's,  142 

for  occlusion  models,  142 
Mechanico-anatomical  antagoni- 

zation  in  vulcanite  dentures,  241 
Metal  base-plate,  133 
Mineral  wax,  57 

Model  for  artificial  velum,  444,  445 
contour,    123.     See  also  Occlu- 
sion models, 
contouring,  technique  of,  472 
dentures,  246 

antagonization  of,  proving  of, 

247 
conversion  of,  into  vulcanite, 

249 
deglutition  test  for,  247 
equalized  pressure  test  for,  247 
finishing  of,  246 
flasking  of,  249 
luting  of,  to  casts,  249 
occlusion  of,  jiroving  of,  247 
opening  of  flask  in,  251 
proving  of,  247 
removal  of,  from  antagonizor, 

249 
for  vulcanite  dentures,  246 
distinction  of,  from  cast,   109 
for  gold  base-plate,  366 
occlusion,  123 
Modelling  compound,  58 
base-plate,  128,  130 
composition  of,  58 
formula  for,  Williams',  58 
for  full  upper  impressions,  86" 
manipulation  of,  58 
Molars  in  vulcanite  dentures,  po- 
sition of,  240 
Molding  for  gold  base-plate,  366, 
370 
of  porcelain  teeth,  315 
sand  for  gold  base-plate,  370 
Molecular  attraction  in  retention, 
284 


Mounting  of  casts,  176 
Mouth,  17 

examination  of,  44 

hands  in,  cleansing  of,  44 
method  of,  45 
mouth  mirror  in,  45 
protection  of  patient  during, 

44 
seating  of  patient  during,  44 
fluids  of,  examination  of,  53 
muscular  attachments  of,  exam- 
ination of,  52,  53 
tissues  of,   glandular,   examina- 
tion of,  52,  53 
mucous,  examination  of,  53 
submucous,  examination  of,  53 
use  of,  41 
Mucous  membrane  in  retention  of 
full  artificial  dentures,  281 
tissues  of  mouth,  examination  of, 
53 
Muscle    trimming    in    full    upper 

impressions,  87 
Muscles  of  expression,  28 
of  mastication,  26. 
of  maxillae,  29 
Mush-bite,  124 


N 


Naso-auditory-meatus  line,  19 

occlusion  models  and,  134 
Nervous  temperament,  464 
Nitrohydrochloric   acid,   vulcanite 

and,  197 
Nomenclature,  Basle   Anatomical, 

32 


Obturatok  for  cleft  palate,  436, 

457 
denture,  453 
Suersen,  453 
velum,  453 
Occlusion  frame,  165 

mounting  of  casts  upon,  177 

use  of,  176 
models,  123 

base-plate  for,  126 

bite  gauges  in,  137 

condyle  path  in,  137 


INDEX 


501 


Occlusion  models,  construction  of, 
133 
definition  of,  123 
for  double  vulcanization,  329 
face  bow  and,  13S 
lines  in,  marking  of,  136 
materials  for,  124 
measuring  instruments  for, 

142 
naso-auditory-meatus  line  and, 

134 
plane  of  teeth  in,  134 
protrusion  of  chin  in,  13.5 
relation  of,  to  esthetics,  46S 
retrusion  of  chin  in,  135 
testing  of,  134 
use  of,  124 

for  vulcanite  dentures,  236,  261 
of  teeth,  33 
Olivian  swager,  363 
Oxyphosphate  of  zinc  cement  for 
repair  of  casts,  121 
vacuum  chambers  and,  290 


PAf'KiXG  for  double  vulcanization, 
335 
of  rubber  for  vulcanite  dentures, 
254 

Palate,  cleft,  436 
soft,  30 

artificial  dentures  and,  30 

Parabolic  curve,  34 

Paraffin  base-plate,  127 

Paris,  plaster  of,  59 

Parker  shot  swager,  363 

Partial  casts,  120 
gold  basc-platc,  396 
impressions,  lower,  104 

upper,  95 
vulcanite  dentures,  263 

Petroleum  heat  for  vulcanite,  233 

Physiognomy,  relation  of,  to  ter'tli, 
459 

"Pickle"  for  swaging  of  gold  base- 
plate, 377 

Pigments     for     dental     porcelain, 
314 

Pink  rubtx-r  for  flouble  vulcaniza- 
tion, 335 

"i'inless"  porcelain  l(!(!th,  322 


Pins,    base    metal,    for    porcelain 
teeth,  327 
countersunk,  for  porcelain  teeth, 

324 
platinum,    for    porcelain    teeth, 
320 
Plain  porcelain  teeth,  319,  322 
Plane  of  teeth,  19 

cubical  block  formation  and, 

20,  21 
in  occlusion  models,  133 
Plaster,  calcined,  60 
casts,  shape  for,  116 
cement,  60 
classification  of,  59 
compound,  Spence's,  111 
manipulation  of,  112 
Portland  cement  in.  111 
compressibility  of,  62,  63 
contraction  of,  62 
expansion  of,  62 
flooring,  60 
hard  finish,  60 
knives,  122 

Wilson's,  122 
of  Paris,  99 
for  casts.  111 
formula  of,  60 
setting  of,  Le  Chatelier's  theorv 

of,  61 
stucco,  60 
wall,  60 
Plate  gold,  364 

porcelain  teeth,  324 
Platinum   base-plate   for   continu- 
ous gum  dentures,  420 
continuous   gum   dcntiu'cs   and, 

416 
pins  for  porcelain  teeth,  320 
Pliers  for  clasjjs,  307 
Polishing  of  aluminum  base-plate, 
354 
brushes  for,  226 
buffers  for,  224 
carborunduin  for,  223 
of  continuous  gum  dentures,  4;>0 
corundum  for,  223 
emery  for,  223 
lathes,  21 S 
I)owder,s  for,  228 
prepared  (ihalk  for,  22.S 
pumice  stone  for,  22S 
stones  for,  223 


502 


INDEX 


Polishing  of  vulcanite,  218 
Polyprene  in  vulcanite,  194 
Porcelain     for     continuous     gum 

dentures,  417,  426 
dental,  311 

alkalies  for,  313 

composition  of,  311 

definition  of,  311 

feldspar  for,  311 

kaolin  for,  313 

materials  for,  311 

pigments  for,  314 

potassium  for,  313 

silica  for,  312 

sodium  for,  313 
soldering  of,  to  gold  base-plate, 

394 
teeth,  310 

anchorage  for,  321 

attachment  of,  to  base,  319 

base  metal  pins  for,  327 

"block,"  325 

body  for,  315 

burning  of,  318 

casting  of,  to  aluminum  base- 
plate, 356 

for  celluloid  models,  323 

classification  of,  318 

countersunk  pin  for,  324 

"diatoric,"  322 

enamels  for,  315 

flux  for,  315 

forms  of,  322 

improvements  in,  326 
Williams',  326 

frits  for,  315 

gum,  319,  325 

"gum  section,"  325 

history  of,  310 

manufacture  of,  314 

molding  of,  315 

"pinless,"  322 

plain,  319,  322 

plate,  324 

platinum  pins  for,  320 

stock  material  for,  324 
Portland  cement  in  Spence's  plaster 

compound.  111 
Potassium  for  dental  porcelain,  313 
Powders  for  polishing,  228 
Prepared  chalk  for  polishing,  228 
Pressure,    atmospheric,    in    reten- 
tion, 272 


Pressure,  equalized,  test  for  model 

dentures,  247 
Price's  artificial  stone,  112 
for  casts,  112 
composition  of,  112,  113 
manipulation  of,  113 

flask,  202 

furnace,  418 
Profile,  concave,  459 

convex,  458 

dental,  458 

straight,  458 
Prosthesis,  definition  of,  454 
Pumice  stone  for  polishing,  228 
Punch,  English  "double,"  394 

single,  394 
Pyrometer,  418 


Q 

Quartz,  312.    See  Silica. 
Quash-bite,  124,  125 


Raphe,  enlarged,  impressions  for, 
94 
maxillary,  examination  of,  48 

Reese's  alloy,  413 

Relief  chamber  for  aluminum  base- 
plate, 342 

Repair  of  vulcanite  dentures,  266 

Replacement  method  for  repair  of 
vulcanite  dentures,  270 

Resinoid    preparations    for    base- 
plate, 131 

Restoration,  unilateral,  489 

Retainers,    soldering    of,    to    gold 
base-plate,  391 

Retention,  adhesion  by  contact  in, 
274,  284 
of  artificial  dentures,  272 
atmospheric    pressure    in,    272, 

287 
balancing  of  plate  in,  304 
base-plate  outline  in,  283 
by  cementation,  309 
by  clasps,  296,  304 
disks  for,  291 
by  ferrules,  297 
of  full  artificial  dentures,  277 


INDEX 


503 


Retention    of    full     artificial    den- 
tures, conditions  affect- 
ing, 277 
fluids  in,  283 
mucous  membrane  in,  281 
shape  in,  283 
size  in,  277 
soft  tissues  in,  277 
submucous  tissue  in,  280 
tension  in,  281 
tone  in,  281 
hydrostatic  law  of,  273 
leverage  in,  27o,  284 
molecular  attraction  in,  284 
of    partial    vulcanite    dentures, 

265 
physical  laws  of,  272 
principles  of,  272,  304 
apphcation  of,  283 
soft  vulcanite  in,  291 
Speyer's  cohesion  surface  forms 

for,  294 
by  tensofriction,  295 
vacuum  chambers  and,  290 
velum  rubber  in,  291 
Rigid  clasps,  297,  302 
R(jck  gypsum,  59 
Roots,  examination  of,  40 
Round  spring  clasps,  310 
Rubber,  183.    See  Caoutchouc, 
for  artificial  velum,  449 
mallet  for  swaging,  377 
packing  of,    for  vulcanite  den- 
tures, 254 
pink,   for  double  vulcanization, 

335 
velum,  291 


S 


Safety-valvk  for  vulcanizer,  207 
Sand,  molding,  for  gold  base-plate, 

370 
•Sanguine  temperament,  463 
Schwartz  method  of  rigid  cla.sps, 

303 
Scrapers,  vulcanite,  218 
Sel«;nite,  59 
Separating  fluids  for  impros.sions, 

114 
Setting  of  plaster,   I.c  Chafelier'.s 

theory  of,  01 


Sheetiron  method  for  removal  of 
teeth   from   \ailcanite   dentures, 
265 
Shrinkage  in  continuous  gum  den- 
tures, 427 
Silex  method  in  cast  for  vulcanite 

dentures,  253 
Silica,  312 

compo.sition  of,  312 
for  dental  porcelain,  312 
preparation  of,  312 
u.se  of,  312 
Single  punch,  394 
Snow's  antagonizor,  170 

mounting  of  casts  upon,  177 
bite-gauges,  137 
face  bow,  138 

interdental  splints  and,  432 
flask    for     interdental     splints, 
432 
Sodium  for  dental  porcelain,  313 
Soft  palate,  30 

ti.ssuos  in  retention  of  full  arti- 
ficial dentures,  277 
vulcanite,  291 
Solder   for   continuous    gum   den- 
tures, 421 
gold,  364 
Soldering  of  gold,  382 
Spatulas  for  wax,  198 
Spec,  curve  of,  21 
Speech,  41 
teeth  and,  42 
artificial,  42 
lo.ss  of,  42 
Spcnce's     plaster     compound     for 
casts,  111 
for     double     vulcanization, 

334 
for  partial  gold  base-i)lates, 

399 
in  vulcanite  dentures,  2()1 
Speyer's  cohesion  surface  forms  for 

retention,  294 
Splints,  interdental,  431 
Spring  clasps,  297,  298 
Sj)rue  formers  for  aluminum  ijase- 

I)late,  344 
Staining  of  teeth,  477 
Star  vulcanite  flash,  201,  202 
Slay  clasps,  296,  297 
Steam  gauge  for  vulcanizer,  207 
pressure  in  vulcanizr^r,  212 


504 


INDEX 


"Sticking  up"  of  artificial  dentures 

281 
Stones  for  polishing,  223 

use  of,  228 
Straight  profile,  458 
Stucco  plaster,  60 
Submiicous  tissues  of  mouth,  exam- 
ination of,  53 
in   retention  of  full  artificial 
dentures,  280 
"Suction"  plate,  274 
Suersen  obturator,  451 
Sulphur  in  vulcanite,  194 
Surfaces,  mandibular,  size  of,  sig- 
nificance of,  49 
maxillary,  size  of,  significance  of, 
49 
Suture,  maxillary,  examination  of, 

48 
Swaged  aluminum  base-plate,  358 
Swaging  of  aluminum  by  die  and 
counter-die  method,  359 
of  full  lower  gold  base-plate,  379 
of  gold,  365 

base-plate,  365,  375 
method   for   partial   gold   base- 
plates, 398 


Tang  attachment  for  bar  lower, 

410 
Teeth,  30 

anterior,  loss  of,  in  partial  upper 
impressions,  95 

arrangement  of,  475 

artificial,  speech  and,  42 

classification  of,  30,  31,  32 

color  of,  475 

coloring  of,  480 

eruption  of,  37 

development  of  jaws  and,  38 
order  of,  37,  38 

esthetics  and,  475 

examination  of,  46 

form  of,  475 

function  of,  30 

gold  filling  and,  476 

grinding   of,    in   vulcanite   den- 
tures, 236,  262 

individualization  of,  476 

loss  of,  importance  of,  42 


Teeth,  loss  of,  mastication  and,  43 
results  of,  43 
speech  and,  42 
occlusion  of,  33 
parabolic  rows  of,  30 
plane  of,  19 

in  occlusion  models,  134 
porcelain,  310 
posterior,  loss  of,  in  partial  upper 

impressions,  98 
relation  of,  to  physiognomy,  459 
removal  of,  from  vulcanite  den- 
tures, 265 
setting  up  of,  in  vulcanite  den- 
tures, 236,  237 
size  of,  475 

and  spaces,  alternating,  in  par- 
tial upper  impressions,  98 
speech  and,  42 

for  spring  clasps,  form  of,  299 
staining  of,  477 

by  Lenox  mineral,  478 
materials  for,  478 
metallic  oxides  for,  478 
technique  of,  479 
view  of,  as  truncated  cone,  36 
Williams'  truebite,  488 
Temperaments,  462 
bilious,  463 

classification  of,  463,  467 
definition  of,  462 
lymphatic,  463 
nervous,  464 
sanguine,  463 
Temporomandibular    articulation, 

23 
Tensofriction,  295 

retention  by,  295 
Thermometer  for  vulcanizer,  207, 

214 
Time-regulator  for  vulcanizer,  210 
Tin  base-plate,  126,  413 
alloys  for.  Bean's,  413 
Kingsley's,  413 
Reese's,  413 
Watt's,  413 
Weston's,  413 
casting  of,  413 
metal  for,  413 
technique  of,  413 
Watt's  flask  for,  413 
method    in    cast    for    vulcanite 
dentures,  253 


INDEX 


505 


Tinfoil    for  double   vulcanization,    \ 

331 
Tongue,  27 

function  of,  27 
Trays,  imj^ression,  63 
Triangle  i)oint,   anterior,   i)atli  of 

motion  of,  determination  of,  152 
Trimmers,  vulcanite,  218 
Truebite  teeth,  \Mlliams',  488 


U 


Upper  impressions,  full,  technique 
of,  69 
partial,  95 
Unilateral  restoration,  489 
vacuum  chambers,  291 


Vacuum  chambers,  290 

for  aluminum  base-plate,  342 
attachment  of,  290 
bilateral,  291 
for  castings,  290 
construction  of,  290 
edges  of,  290 
forms  of,  291 
indications  for,  294 
materials  for,  290 
oxyphf)sphate  of  zinc  cement 

and,  290 
retention  and,  290 
soft  vulcanite  for,  291 
unilateral,  291 
velum  rubber  for,  291 
Varnishes  for  impressions,  115 
Vault,  dental,  distinction  of,  from 
dental  arch,  47 
examination  of,  47 
value  of,  48 
flat,  difficult,  in  full   ui)per  im- 
pressions, 80 
in  full  up[)er  impressions,  80 
high,  in  fidl  ujjper  irnpnissions, 

79,  60 
maldcvelopment  of,  48 
Vegetable  wax,  57 
Velum  artificial,  436 
cjist  for,  441 
ff.r  cleft  palate,  43r) 


'lum    artificial,   construction    of, 

439 
finishing  of,  449 
impression  for,  439 
Case's  method  of,  439 
for  retaining  base-plate  for, 
449 
model  for,  444,  445 

adjustment   of,    to    mouth, 

446 

flasking  of,  446 
metal  encasement  for,  447 
retaining  base-plate  for,  449 
rubber  for,  449 
obturator,  453 
palati,  30 

rubber  in  retention,  291 
for  vacuum  chambers,  291 
Vulcanite,  183,  186 
advantages  of,  197 
in  artificial  dentures,  197 
attachment  of  swaged  aluminum 

base-plate  to,  360 
base-plate,  131 

advantages  of,  131 
disadvantages  of,  131 
technic|ue  of,  132 
buffing  of,  228 
chemistry  of,  191 
chisels,  218 

composition  of,  188,  193 
dentures  antagonization  in,  241 
proving  in,  242,  243 
base-plates  for,  234 
bicuspids  in,  intercuspation  of, 

240 
casts  for,  234 

silex  method  in,  253 
tin  method  in,  253 
compensating  curve  in,  242 
complete,  233 
contour  model  for,  261 
conversion     into,     of     model 
dentures,  249 
■  diagnosis  for,  233 

I  examination  of  mouth  for,  261 

I  finishing  of,  258 

flask  in,  closing  of,  256 

opening  of,  251 
impression  for,  234 

tray  in,  removal  of,  261 
insertion  of,  260 
lower,  construction  of,  2W 


506 


INDEX 


Vulcanite  dentures,  lower,  impres- 
sions for,  261 
mechanico-anatomical    antag- 

onization  in,  241 
model  dentures  for,  246 
molars  in,  position  of,  240 
mounting  on  antagonizor  in, 

236 
occlusion  and  contour  models 
for,  235 
model  for,  261 
partial,  263 
flasking  of,  263 
finishing  of,  265 
retention  of,  265 
prognosis  for,  233 
removal  of,  from  flask,  258 
of  teeth  from,  265 
flame  method  for,  266 
glycerin  method  for,  266 
sheetiron  method  for,  265 
repair  of,  266 

additions  to  old  plates  for, 

270 
fusible   metal    method    for, 

269 
ironing-in  method  for,  271 
replacement     method     for, 

270 
wax  method  for,  266 
rubber  for,  packing  of,  254 
short  balancing  curve  in,  242 
Spence  plaster  compound  in, 

261. 
teeth  in,  grinding  of,  236,  262 
setting  up  of,  236,  237 
grinding  in,  236 
upper,  construction  of,  260 

impressions  for,  261 
wax  casts  in,  removal  of,  262 
disadvantages  of,  197 
double    vulcanization    of,    328. 

See  Vulcanization,  double, 
files  for,  217 
flasks,  200 

formula  for,  chemical,  196 
formulas  for,  188 
glossing  of,  229 
grinding  of,  218 
heat  for,  229 
alcohol,  231 
Bunsen  burner,  230 
gas  stove,  231 


Vulcanite,  heat  for,  gasoline,  231 

jeweller's  triple  burner,  230 

petroleum,  233 
history  of,  186 
hydi'ogen  sulphide  in,  194 
nitrohydrochloric  acid  and,  197 
polishing  of,  218 
polyp rene  in,  194 
porosity  of,  190 
properties  of,  physical,  190 
repair  of,  191 
scrapers,  218 
soft,  for  vacuum  chambers,  291 

in  retention,  291 
solvents  of,  190 
sulphur  in,  194 
trimmers,  218 
Weber's  experiments  with,  191- 

193 
work,  instruments  for,  198 
Vulcanization,  257 
chemistry  of,  257 
double,  328 

base-plate  for,  329 

cast  for,  328 

finishing  of,  337 

flfask  for,  333 

separation  of,  334 
Wilson's,  333 

flasking  for,  333 

preparation  of  case  for,  330 

impressions  for,  328 

mounting  of  teeth  for,  329 

occlusion  and  contour  models 
for,  329 

packing  for,  335 

peripheral  strings  in,  334 

pink  rubber  for,  335 

proving  of  contour  of,  330 

separating  cloth  for,  336 

Spence's     plaster     compound 
for,  334 

technique  of,  328 

temperature  for,  337 

tinfoil  for,  331 

Walker's    granular    gum    for 
335 
temperature  for,  257 
Vulcanizers,  206,  257 
blow-off  for,  207 
gas-regulator  for,  207 
leakage  in,  215 
Lewis  cross-bar,  206 


INDEX 


507 


\'ulcanizcr.s,  nianifoldor  for,  207 
oporation  of,  20S 
placing  of  flask  in,  257 
removal  of  flask  from,  258 
safety-valve  for,  207 
steam  gauge  for,  207 
pressure  in,  212 

elastic  force  of,  213 
thermometer  for,  207,  214 
time-regulator  for,  210 
operation  of,  212 
setting  of,  211 
use  of,  210 
Vulcanizing,  technique  of,  215 


W 

Walk  er-Christenson-S  now 
method  of  condyle  path,  141 

Walker's  antugonizor,  ItiS,  169 
granular  gum  for  double  vulcan- 
ization, 335 

Wall  plaster,  60 

\\'arping  in  soldering  of  gold  base- 
plates, 392 

Watt's  alloy,  413 
flask,  413 

Wax,  56 

characteristics  of,  56 
and  compounds  for  casts,  113 
instruments  for,  198,  199,  200 
method  for  repair  of  vulcanite 

dentures,  266 
mineral,  57 

composition  of,  57 


Wax  model  base-plate,  for  alumi- 
num base-plate,  342 
removal  of,  from  flasks,  251 
spatulas  for,  198 
vegetable,  57 
Wax-bite,  124 
Weston's  alloy,  413 
"\\'heels,  carborundum,  224 
White  wax,  56 

Whitney's  vulcanite  flask,  202 
Williams'  forms  of  porcelain  teeth, 
326 
formula     for     modelling     com- 
pound, 58 
true-bite  teeth,  488 
Wilson's  flask  for  double  vulcani- 
zation, 122 
plaster  knife,  122 
vulcanite  flask,  202 
Wire    method,     double,     for    bar 
lower,  405 
single,  for  bar  lower,  402 
reenforcing,  for  continuous  gum 
dentures,  423 


Yellow  wax,  56 


Zinc  for  die,  372 

oxyphosphatc    of,    cement, 
repair  of  casts,  121 


for 


%' ' 


v\ 


^4'l' 

f'.K:.:^'/,Z. 

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DATE  BORROWED 

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DATE  BORROWED 

DATE  DUE 

C28(S46)M2B 

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Wilson 


W69 


Manual  of  dental  prosthetics 


p  COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx) 

A  iiicinuji:  of  dental  prosthetics, 

2002384752 


